C S HA I CNG

1.1. HA HU C CHT HU C

1.1.1. c im v s pht trin ca ho hc hu c.

i tng nghin cu ca ho hc l nhng cht ho hc ring bit v s bin i ca

chng. Mt lnh vc c bn ca ho hc l ho hc hu c nghin cu cc hp cht ca cacbon

vi cc nghin t khc, ch yu l hp cht ca cacbon vi Hyr, Oxi, Nit, Phtpho, Lu

hunh v Halogen.

Nhiu hp cht hu c c con ngi bit rt lu nh: dm (axit axetic lng), mt s

thuc nhum, ru etylic, cc hp cht axit oxalic, axit xitric, axit tactric v mt s baz hu c

(cc ancaloit) c tch t ng thc vt vo cui th k th 18 v u th k th 19. Thi

im ny cng c tnh l thi im u ca mn ho hc hu c.

th k th 18 v th k th 19, ngi ta cho rng ho hc ca th gii cc cht SNG

khc vi th gii ho hc ca cc cht cht, l c th sng c cu to t nhng hp cht c

bit do mt ngoi lc sng (Tri, Cha, Pht) to nn m cc cht bn thn con ngi

khng th tng hp c. Nhng nhng pht hin th k 19 cho thy rng tt c cc hp cht

cu to nn c th ng vt v thc vt u c thnh phn ging nhau ph v s khc bit

gia ho hc ng vt v thc vt. Hai lnh vc nghin cu ny st nhp vo nhau v hnh

thnh mn ho hc hu c. Nh bc hc Thy in Berceluyci (1779-1848) c rt nhiu

cng trong lnh vc st nhp ny. Sau ng, nh bc hc Lavuaze, bng nhng phng php

phn tch nh lng pht hin c mt s nguyn t mi, xc nh c nguyn t lng

ca nhiu nguyn t, t nn mng cho hin tng ng phn. Nh ho hc c Beler bng

phn ng thu phn hp cht ixianua (v c) thu c axit oxalic (hu c) nm 1824 v t

xinaoxit amoni (v c) thu c ur (hu c) nm 1828 ph v s phn bit gia hp cht

v c v hu c. iu ny cng chng minh rng cc hp cht hu c c th thu nhn c

bng con ng tng hp m khng cn s tham gia ca mt ngoi lc huyn b no c. iu

c khng nh bng cc cng trnh ca Buttlerp tng hp cc hp cht ng t

formalin (1861), Faray thu nhn c bezen (1825), Zinin tng hp c anilin t nitrobezen

(1842) v t anilin thu nhn c cc hp cht mu vo nhng nm 50 ca th k 19. Cng

vo nhng nm ny Gmelin a ra nh ngha ho hc hu c l ho hc cc hp cht

cacbon v n ti n ngy nay.

1.1.2. Cu to ca cc hp cht hu c.

Chng 1

2T nh ngha trn y xut hin mt vn ln l ti sao t hng trm nguyn t bit

ch c cacbon to thnh nhiu hp cht nh vy?

Th nht: do hin tng ng phn c Berceluyci pht hin cho tt c cc cht ho

hc m c bit l cht hu c c th tn ti nhiu hp cht khc nhau c cng thnh phn

nguyn t, cng phn t lng nhng khc nhau v cu to. V d: C20H42 c 366.319 hp cht

khc nhau, C30H62 tn ti 4.111.846.768 hp cht khc nhau.

Th hai: do hin tng ng ng - tn ti cc hp cht ho hc m thnh phn ca mi

cht ch khc nhau bi mt nhm CH2 (mtylen).

Th 3: do hin tng ng cp - cc hp cht c cu to cng mt s nguyn t

cacbon nh nhau nhng hp cht sau c t hn hp cht trc 2 nguyn t Hyr (tan C2H6,

tylen C2H4, axetylen C2H2).

Vy ti sao cc hp cht hu c li tn ti di cc dng ng ng, ng phn?

Trong cc thuyt a ra gii thch vn ny ca nhiu nh bc hc thuc nhiu th

h khc nhau c th lu mt vi gi thit sau y:

Thuyt kiu ca Zerar cc hp cht c phn b theo cc kiu H2O, HCl, H3N, H2.

y ch cn thay th hyr ca cc kiu bng phn gc hu c th ta s thu c cc hp cht

khc nhau.

V d:

H

HO

CH3

HO

C2H5

HO

C2H3O

HO

nc mtanol tanol axit axetic

H

Cl

CH3

Cl

C2H5

Cl

C2H3O

Clhyrclorua mtylclorua tylclorua axtylclorua

CH3

H

H

H

C2H5

H

C2H3O

Hhyro mtan tan axtanhyt

Nm 1851, Viliamxn a ra thuyt raical ca nhiu nguyn t - tc l cc raical c

kh nng thay th 2 hoc nhiu hyr trong cc kiu.

3V d: axit aminaxtic l kiu H2O v NH3

H

C2H3OO

H

HN

c bit quan trng l kiu mtan ca Kkuk

HHHH

C

Kkul s dng khi nim ho tr ca nh ho hc Anh Frankland cho nguyn t

cacbon 1857. T vic cng nhn nguyn t cacbon c ho tr 4, Kkul i n kt lun l

nguyn t cacbon c kh nng lin kt vi nhau.

V d: tan c th vit:

HHH

C

CH3

Nh vy cacbon lin kt vi nhau to thnh cc mch di ngn khc nhau.

Mt trong nhng ng gp quan trng cho thuyt cu to cc hp cht hu c l

thuyt cu to ca Buttlrp (1861): bn cht ho hc ca mt phn t ca mt cht c xc

nh bi bn cht cc nguyn t c hp thnh, bi s lng ca chng v bi cu to ho

hc. T ni dung ca thuyt ta c th rt ra cc kt lun sau:

1. Cc nguyn t trong phn t khng phi sp xp hn n, v trt t, chng kt hp

vi nhau theo mt trt t xc nh, theo ng ho tr ca chng.

2. Tnh cht ca cc cht khng nhng ph thuc vo thnh phn nguyn t, vo s

lng nguyn t ca cc nguyn t m cn ph thuc vo cu to ho hc ca chng na.

3. Cu to ca cc cht c th xc nh c khi nghin cu tnh cht ca chng. Cu

to ho hc ca mi cht c th biu th bng mt cng thc ho hc nht nh gi l cng thc

cu to.

Thuyt cu to Buttlrp chnh l nn tng cho s pht trin ca ho hc hu c t nm

1861 n nay. Bng cc phng php ho hc ngi ta xc nh c cu to ca nhiu hp

cht khc nhau. Ngy nay, tuy cc phng php ho hc vn cn c ng dng trong thc t

nhng xut hin cc phng php vt l nh khi ph, ph cng hng t nhn, ph in

4tgip cho cc nh ho hc xc nh nhanh chng v chnh xc cu to ca cc hp cht ho

hc.

Tm li, s hnh thnh khi lng khng l cc hp cht hu c l do kh nng to

thnh dy ng ng, ng phn, kh nng to thnh nhng mch di (c th ni l v tn), kh

nng to lin kt bn vng vi cc tc nhn electronphin (nh hyr), vi tc nhn nucleophin

(nh halogen, xy, Lu hunh, Nit..) ca nguyn t cacbon.

1.1.3. Cc phng php biu din trong ho hc hu c.

Nh ta bit ho hc v c nghin cu ch yu cc hp cht phn cc v cc lin kt

ho hc phn cc. Tri li ho hc hu c nghin cu ch yu cc hp cht khng phn cc v

cc lin kt khng phn cc. Thuyt in ly trong nhng nm u ca th k 20 t nn tng

cho l thuyt cu to ion ca cc mui v cc cht in ly. S pht minh electron v cc nh

lut nh lng ca qu trnh in ly l c s cho thuyt ho tr in t. Theo cc thuyt ny

mt hp cht in ly c cu to t cation v anion. Cation l nguyn t kim loi b mt in

t, cn anion l nguyn t khc nhn thm in t. L thuyt ny c Kosel ng dng cho

nhiu hp cht v nhiu qu trnh trong ho hc v c (1917). Mt khc Kosel cng nhn thy

rng, i vi cc cht khng phn cc nh H2, O2, N2, hyrcacbon th thuyt in ly khng

thch hp m phi tm kim nhng thuyt ho hc khc. iu c Luit gii thch bng

lin kt cng ho tr (1916) c to thnh do cp in t gp chung gia cc nguyn t. Theo

Luit, lin kt gia cc cht khng phn cc c biu din nh sau:

H H H CH

HH H C

H

HC HH

HH C

H

HCH

HO H

H2 CH4 C2H6 CH3CH2OH

y cp in t c th thay th bng gch ngang (-). Do cc hp cht lin kt i

hay lin kt ba c th biu din:

H CH

C HH

hoc C C

H

H

H

H

H C C H hoc H C C H

1.1.4. Phn loi cc hp cht hu c.

Cc hp cht hu c c phn loi theo cu to ca chng, c trng bi cc lin kt

gia cc nguyn t cacbon vi nhau. Cc hp cht c cha cc nguyn t khng phi l cacbon

c xem nh dn xut ca hyrcacbon m trong nguyn t hyr c thay th cc

5nguyn t khc. Tt c cc hp cht hu c c chia lm 2 nhm ln: cc hp cht mch h

v cc hp cht mch vng.

Cc hp cht mch h l nhng hp cht bo:

Mch thng khng phn nhnh (normal).

H C C C C C

H H H H H

H

H H H H HH C C C C C

H H H H H

C

H H H H H

C C H

H

H

H

H

H

Hn-pentan n-ctan

Mch phn nhnh:

C

H

H

H

C

CH3

CH3

C

H

H

Hnepentan

C

H

H

H C

H

CH3

C

H

C

H

H

H

Hizpentan

Cc hp cht khng no (cha ni i, ni ba): CH

H

C

H

C

H

C H

H

CH3CH2 C CH

butaien-1,3butin-1

Cc hp cht vng gm:

Vng ring bit-ch c nguyn t cacbon tham gia ng vng:

CC C C C

C C C CC C

C C

C CC

D vng-cc nguyn t tham gia ng vng ngoi nguyn t cacbon cn c cc nguyn

t khng phi l cacbon nh Oxi, NitCng tng t nh cc hp cht mch h, cc hp cht

mch vng cng c vng khng no cha ni i hoc ni ba. c bit, mt trong nhng vng

khng no rt quan trng l loi vng thm-vng cha 6 nguyn t c ba ni i lin hp ca

cacbon hoc cacbon vi cc nguyn t d t.

NNNaphtalen KinlinBenzen Piriin

Trong loi hp cht thm ny cn c loi vng 5 nguyn t cha 2 ni iv mt nguyn

t d t cha cp in t t do:

Pirol Furan Tiphen

N

HO S

61.1.5. Cch gi tn cc hp cht hu c .

Trong ho hc hu c cho n nay tn ti nhiu cch gi tn khc nhau. gi cc dy

ng ng ca hyrcacbon, ngi ta thng s dng tn gi ca cc hp cht n gin nht.

V d hyrcacbon dy mtan, hyrcacbon dy tylen, hyrcacbon dy axtylenTt c cc

hp cht hu c khc cn li c xem nh l dn xut ca hyrcacbon. gi tn cc hp

cht hu c ring bit, thng s dng cc danh php: danh php thng thng, danh php Gi-

ne-v (1892), danh php IUC (International Union Chemistry) 1950, danh php IUPAC

(International Union of Pure and Applied Chemistry) 1957

A. Danh php thng thng:

Gi tn cc hp cht theo lch s thu nhn c, theo ngun gc ca nguyn liu ban

u, theo phng php tng hpV d: kh m (t m), axit focmic (focmic-kin), vanilin

(vani-cy vani)Nhiu cht c gi tn ca nh bc hc thu nhn c n. V d xton

Micler, hyrcacbon TitibabinMt s tn gi thng thng c s dng rt rng ri trong h

thng tn gi th gii. V d tn gi ca dy ng ng ankan t C5 tr i c phn gc l s m

h latinh cng thm ui an (pentan, hexan, heptan) nhng 4 hp cht u (mtan, tan,

propan, butan) li l tn gi thng thng v phn gc khng phi l s m h latinh.

B. Danh php IUPAC:

Gi tn cc hp cht mch h:

1. Gi tn 4 hp cht u ca hyrcacbon no l: mtan, tan, propan, butan. Gi tn

cc hp cht tip theo ca dy ny bng phn gc l s m h latinh cng ui an: pentan,

hexan, heptan, octan, nnan, kanTn gi chung ca hyrcacbon mch thng no l ankan.

2. Cc raical (phn gc) c ho tr I c to thnh t hyrcacbon no mch h bng

cch tch i mt nguyn t hyr u mch c gi tn bng cch thay ui-an bng ui

yl.

Vd: CH3CH2CH2CH2CH3 CH3CH2CH2CH2CH2-

Pentan Pentyl

CH3-CH2-C7H14-CH3 CH3-CH2-C7H14-CH2-

kan kyl

3. Mch di nht c nh s t u ny n u kia bng ch s latinh sao cho v tr

cc nhm mch nhnh c tng cc ch s l nh nht. Trng hp khi nh s t u ny n

u kia m thu c mt s dy ch s ca cc nhm mch nhnh khc nhau th phi sp xp

chng li theo th t tng dn. Dy c tng cc ch s nh nht c xem l dy c ch s u

nh nht.

7V d:

CH3 CH2 CH CH2 CH3CH3

CH3 CH CH2 CH2 CH3CH3

3-mtylpentan 2-mtylpentan (khng c 4-mtylpentan)

CH3 CH CH2 CH CH CH3CH3 CH3 CH3

2,3,5-trimtylhexan(khng c 2,4,5-trimtylhexan) CH3 CH2 CH2 CH2 CH

CH3

CH3CH2CH2CH3

CH2CH2CH

5-mtyl-4-prpylnonan(khng c 5-mtyl-6-prpylnonan)

4. Cc phn gc (raical phn nhnh ho tr 1) c gi tn bng cch

thm vo mch thng khng phn nhnh di nht ankyl (bt u t pha c ho tr t do s 1) tn

gi cc mch nhnh.

V d: CH3CH2CH2CH2CH(CH3)- CH3CH2CH2CH(CH3)CH2-

1-mtylpentyl 2-mtylpentyl

Mt s nhm gi tt nh sau:

(CH3)2CH- (CH3)2CHCH2- CH3CH2CH(CH3)- (CH3)3C-

Izprpyl izbutyl secbutyl tecbutyl

(CH3)2CHCH2CH2- (CH3)3C-CH2- CH3CH2C(CH3)2-

Izpentyl nopentyl tecpentyl

5. Nu c 2 nhm mch nhnh khc nhau tr ln th c th gi chng theo th t ch ci

hoc theo phc tp ca nhm ( ln khng gian ca nhm).

V d: Theo vn ch ci:

CH3 CH2 CH2 CH CH CH2 CH3C2H5 CH3

Hai nhm tyl (C2H5) v mtyl (CH3) th ch E ng trc ch M nn gi l 4-tyl-3-

mtylheptan.

Theo phc tp ca nhm:

Nhm c s nguyn t cacbon nhiu phc tp hn nhm c s nguyn t cacbon t:

(CH3)3C- < CH3CH2CH2CH2CH 2-

Nhm ph c ch s nh, t phc tp nhm c ch s ln:

CH3CH2CH(CH3)CH(C2H5)CH2- < CH3CH2CH(C2H5)CH(CH3)CH2-

Gc no nh hn gc khng no:

8CH3CH2CH2- < CH3CH=CH-

Gc c ch s v tr khng no nh s nh hn v tr ln:

CH3CH=CH- < CH2=CH-CH2-

6. Khi c mt nhiu nhm th ging nhau ta dng cc tip u ng: i-(2), tri-(3), ttra-

(4), penta-(5), hexa-(6), hepta-(7)V d:

CH3CH2C(CH3)2CH2CH3 c l 3,3-imtylpentan.

7. Cc hp cht khng no c mt ni i, gi tn bng cch thay ui an bng ui en,

2 ni i thnh aien, 3 ni i thnh atrienTn gi chung cho cc hp cht l anken,

ankaien, ankatrien

V d: Hp cht CH3CH2CH2CH=CH-CH 3 gi l 2-hexen

CH3CH=CHCH2CH=CH2 gi l 1,4-hexaien

Ch : CH2=CH2 tylen v : CH2=C=CH2 allen khng theo h thng danh php IUPAC.

Bng cch chuyn i tng t nh vy gi cc hp cht cha ni 3: c 1 ni 3 th

i ui an thnh ui in, c 2 ni 3 th i thnh ui aiin, c 3 ni 3 th i thnh

atriin

Tn gi axtylen l danh php thng thng nn n khng thay i theo quy lut trn.

Cc gc anken c ho tr I c gi bng cch thm vo phn ui t -enyl, -

ienylcn cc gc ankin c ho tr I th thm vo ui inyl, -iinyl

V d: CH3 CH CH CH3 CH CH CH2 HC C HC C CH2

1-prpenyl 2-butenyl tinyl 2-prpinyl 8. Gi tn cc hp cht vng tng t nh cc hp cht mch h c thm tip u ng

xyclo-.

V d:

CH2

CH2 CH2

CH2

CH2 CH

xyclprpan xyclhexan xyclhexylxyclprpyl

C

CCH2

CH2

CH2CH2

H2

H2

C

CCH2

CH2

CHCH2

H2

H2

1.2. CHT TINH KHIT

Khi nim v cht nguyn cht (mt cht n gin hay mt hp cht) l nhng cht c

cu to t nhng phn t ging nhau. Nhng trong thc t kh c th thu nhn c nhng cht

nh vy, do cc nh ho hc hu c tnh rng nhng cht c cha 99% cht hu c c gi

l cht ho hc tinh khit. nh gi tinh khit ca cc cht, thng dng cc phng php

9vt l nh nhit nng chy, nhit ng c, nhit si p sut nht nh, ch s khc

x, quay cc, cc loi quang ph

1.2.1. Cc phng php thu nhn cht tinh khit.

1.2.1.1. Phng php kt tinh.

y l phng php quan trng nht tinh ch cc cht rn. Ta ho tan n mc bo

ho sn phm th trong mt dung mi thch hp nhit cao, lc nng dung dch khi cc

thnh phn khng ho tan ri ngui v nh th l hp cht s kt tinh li di dng tinh khit

hn.

a. La chn dung mi: trong dung mi c la chn hp cht phi t tan nhit thp

nhng tan tt khi un nng cn cc tp cht nu tan cng nhiu th cng tt. Theo kinh nghim,

thng mt cht c ho tan tt trong dung mi c cu trc ho hc tng t vi n, nht l

i vi cc hp cht c cu trc n gin. V d: cc hyrcacbon tan tt trong cc dung mi

thuc loi hyrcacbon, te, cn cc anehyt, phnol, ancol, axit cacbxylic tan tt trong H2O,

ancolTt nhin dung mi c la chn khng c lm thay i cht ho tan v mt ho

hc.

b. Cch tin hnh: trc ht ta un nng hp cht cn kt tinh trong mt lng dung mi

khng ho tan lng cht , sau ta un si dung mi v qua sinh hn cn thn cho

thm dung mi vo cho n khi ho tan hon ton cht kt tinh trong dung mi dang si. Lc

nng dung dch, lm lnh s thu c cht rn tinh khit hn.

1.2.1.2. Phng php chng ct.

Chng ct l phng php tch v tinh ch quan trng nht i vi cc cht lng. Trong

trng hp chng ct n gin, ta cung cp nhit cho mt cht lng n khi cht si v hi

ngng t c to thnh trong mt ng sinh hn. Hng ly cht lng ta c cht lng

chng ct tinh khit hn. V trong trng hp ny ch c mt tng (tc l hi) chuyn ng

nn ta gi l chng ct cng dng hay chng ct n gin. Ngc li nu c mt phn hi c

ngng t chy ngc li vi dng hi v li nh vo bnh ang si ta gi l chng ct ngc

dng (cn gi l chng luyn rectification).

a. Chng ct n gin: Tin hnh chng ct n gin hp l hn c l khi nhit si

vo khong 40-150oC ( cao hn 1500C cc cht hu c d b phn hu, thp hn 400C d b

mt mt nhiu). V vy cc cht lng si cao hn 1500C phi tin hnh chng ct di chn

khng.

Chng ct n gin ch thch hp vi cc hn hp lng gm cc cu t c nhit si

khc xa nhau.

10Ch khi tin hnh phi iu chnh sao cho tc chng ct trong mt giy khng qu 1

n 2 git ri xung bnh hng. Khi chng ct phi lp ng cong cho qu trnh si- tc l v

ng biu din s thay i nhit vi lng cht lng chng ct c T= f(x) ml.

b. Chng ct phn on (tinh ct): Trng hp ny p dng khi chng ct n gin

khng tch c hn hp ra khi nhau (thng l khi hiu s im si ca cc cht nh hn

800C). Khi tin hnh bng phng php ny trong ct chng ct pha di c nhit cao

hn pha trn nn hi c nhit cao i t di ln truyn nhit cho cht lng ngng t t

trn xung, lm cho mt phn cu t d bay hi trong cht lng b ngng t li, tip tc bay hi

ln 2, ln 3cn mt phn cu t kh bay hi trong pha hi b ngng t thnh lng v tip tc

i xung gn di ct ct. Kt qu ca qu trnh lp li nhiu ln nh vy cho ta thu c cht

lng ct ra tinh khit hn v cht lng cn li trong bnh ct cng tinh khit hn.

c. Chng ct li cun bng hi nc: Nu hai hp cht khng ho tan vo nhau th p

sut hi ca chng khng nh hng n nhau. Ta c:

fA = pA

v p = pA + pB

fB = pB Trong fA, fB l p sut ring phn ca A, B.

pA, pB l p sut hi bo ho ca A, B tinh khit cng nhit T0C.

Mt cht si nhit m p sut hi ca n cn bng vi p sut hi ca kh quyn.

Nh vy nu ta un hai cht lng khng ho tan vo nhau th hn hp s si nhit m

tng p sut hi ca 2 cht lng bng p sut kh quyn. iu c ngha l im si ca hn

hp nh vy bao gi cng thp hn im si ca cu t c im si thp nht. Trong thc t

thng dng cht lng th 2 l nc, v vy chng ct hn hp nh vy c th tin hnh

nhit thp hn 1000C. Tt nhin nc khng c trn ln v tc dng vi cht cn chng

ct.

Cch tin hnh: Ta dn hi nc c to ra t mt bnh bng kim loi hoc thu tinh

vo y ca bnh ct hnh cu. Trc cn un dung dch cn chng ct cho ti gn si tr

lc cho qu trnh ct. Bnh thu sn phm s thu c hai lp cht lng (nc v cht cn tinh

ch) c tch ra bng phng php gn hoc bng xiphng. Ni chung ta chng ct n khi

no cht lng ct khng cn tch thnh hai lp na. i vi cht lng c nhit si cao c th

thay nc bng tylen hoc glyxrin.

1.2.1.3. Phng php thng hoa.

11Phng php thng hoa l phng php m trong ngi ta lm bc hi cc cht rn v

sau ngui chng c th ngng t trc tip li di dng cht rn m khng phi lm nng

chy chng.

1.2.1.4. Chit.

Chit l vic chuyn mt cht dng ho tan hay dng huyn ph t mt tng ny sang

mt tng khc.

a. Chit cc cht rn: V d chit ng ra khi ma hoc c ci ng. Trong phng

php chit n gin mt ln, ta un nng hp cht cn thit vi dung mi trong mt bnh cu c

sinh hn hi lu, lc nng hoc lng cho trong ri tch cc phn ring ra khi nhau. Trong

phng php chit n gin nhiu ln, ngi ta lp i lp li nhiu ln nh m t trn.

b. Chit cht lng, chit cc dung dch huyn ph: Ta cho dung dch nc hoc huyn

ph nc chit vo mt phu chit v cho thm dung mi chit vi khong 1/5 n 1/3 th

tch cht lng vo phu. ng kn nt phu chit v lc mnh mt s ln, sau yn,

dung dch phn thnh 2 lp v tch ly lp dung mi. Theo kinh nghim th dng t dung mi v

chit nhiu ln c li hn l chit mt ln vi c lng dung mi chit.

1.2.1.5. Sc k.

Phng php sc k do nh bc hc ngi Nga Svet ln u tin a ra v ngy nay n

c ng dng rt rng ri trong nhiu lnh vc thc t. Phng php sc k gm c cc dng:

sc k giy, sc k ct, sc k lp mng, sc k kh.

a. Sc k giy: y l loi sc k phn b m trong tng ng l hn hp cht cn

tch v tng tnh l nc (hoc dung mi khc nh du silicol, du parafin, du ha) tm ln

giy (xenlul). Ta cho cht ln mt im nht nh trn mt giy (im xut pht), khi tng

ng chy qua, cc cht c tch ra. Ta tin hnh sc k giy trong mt bnh kn m khng

gian c bo ho vi tt c cc cu t ca h dung mi c s dng.

h1h2 h3 H

i lng c trng cho v tr ca cc hp cht sau khi tch l tr s Rf (ratio of front):

khong cch t im xut pht n trung tm vt cht(h)

khong cch t im xut pht n tuyn dung mi (H)Rf

=

b. Sc k ct: Ta cho cht mang (xit silic xp, silicagen, bt xenlul) c tm tng tnh

vo ct, sau ho tan hn hp cht cn tch trong tng ng v cho ln u ct. Sau khi

12dung dch thm vo ct, ta ra vi nhng lng tng ng khc nhau. Ta thu sn phm tch

vo nhng bnh hng khc nhau, lm bay hi ht dung mi v thu ly sn phm tinh khit.

c. Sc k lp mng: y l loi sc k hp ph m trong ta s dng mt ct h di

dng mt hp cht hp ph mng c tri ln mt tm knh. Thng dng nhng tm knh c

(50 x 200mm, 200 x 200mm) lp cht hp ph (silicagen, xt nhm trn t st). Cch

tin hnh sc k lp mng ging nh sc k giy trn y.

d. Sc k kh: y l mt phng php hin i c hiu lc cao m trong hn hp

cht c phn b gia tng tnh (lng) v mt kh tr v vic vn chuyn c tin hnh

trong tng kh. Phng php ch gii hn cho nhng cht d bc hi m khng b phn hu

nhit cao hay trong khi phn hu cho nhng sn phm xc nh di th hi.

Nguyn tc hot ng ca mt my sc k kh: tng tnh (parafin, cc iankyl phtalat,

cc polyglycol) c tm trn mt vt liu mang th rn (xt silic, t st) c t

trong ct tch (ng knh ct khc nhau khong t 6mm n 0,25m). Di mt th hiu p

sut khng i, mt lung kh (hyr, hli, nit, agon, xt cacbon) chy qua ct tch v hn

hp cht cn tch vo u ct c a vo lung kh ny. Dng kh mang cht chy qua ct v

trong qu trnh cc cht c tch ra khi nhau, c o v c ghi nhn bng mt h

thng pht hin thch hp.

My pht hin

Cht cn tch a vo

Kh mang

Kh quyn Thit b hng

T

ng t

nh

My t ghi

S mt my sc k kh.

1.3. Cng thc phn t ca cc cht hu c .

tin hnh xc nh cng thc phn t ca mt cht hu c ta cn phi:

1. Phn tch nh tnh cc nguyn t - tc l xc nh nhng nguyn t no cu to nn

phn t.

132. Phn tch nh lng cc nguyn t - tc l xc nh s lng cc nguyn t ca cc

nguyn t cu to nn phn t v lp cng thc n gin ca phn t.

3. Xc nh phn t lng ca phn t - lp cng thc ng ca phn t.

1.3.1. Phn tch nh tnh cc nguyn t.

a. Pht hin cacbon v hyr: S c mt ca cacbon v hyr c pht hin bng phn

ng t chy hp cht hu c vi xt ng.

(C, H) + CuO------t----- Cu + CO2 + H2O

CO2 thot ra trong phn ng c pht hin bng Ba(OH)2 cho kt ta BaCO3 mu trng,

cn H2O c pht hin bng CuSO4 cho hp cht CuSO4.5H2O c mu xanh.

b. Pht hin Nit: Nu trong hp cht c cha Nit th khi t chy n s ta mi kht

ging nh mi tc chy hoc un vi vi ti xt s ngi thy mi amniac bay ra. Mt phng

php tt hn l un nng chy mu hp cht cn xc nh vi natri kim loi. Nu phn ng xy

ra th s to thnh mui natri xyanua.

Nh vo dung dch ca mui ny mt vi git ca dung dch mui st II v st III, un ti

si v sau khi lm lnh axit ho bng dung dch HCl. Nu c kt ta xanh ph (xanh p-ruyt-

x) th chng t hp cht c nit.

Na (C,N) NaCN

2NaCN FeSO4 Fe(CN)2 Na2SO4

Na4[Fe(CN)6]

Fe4[Fe(CN)6] 12NaCl

4NaCN

FeCl34

+++

+ +

+Fe(CN)2

Na4[Fe(CN)6]xanh ph

HCl

Pht hin halogen: Dng dy ng mng t trn ngn la cho n khi ht ngn la mu

xanh, sau cho mt lng nh mu cht ln u dy ng v t tip. Nu ngn la li xut

hin mu xanh th chng t hp cht c halogen. Ta cng c th pht hin halogen bng cch

un nng chy mu cht vi natri kim loi.

(C, H, X) Na NaX+ Pht hin ion X- bng Ag+ cho kt ta AgX.

1.3.2. Phn tch nh lng cc nguyn t.

Nguyn tc chung: t chy hon ton mt lng c cn chnh xc ca mt hp

cht hu c tinh khit vi mt lng d CuO khan. Cacbon v hyr s chuyn hon ton thnh

kh cacbonic v nc. Dng mt lng xy kh ui ht sn phm t chy vo nhng ng

hp th ring bit: ng ng clorua canxi khan hp th hi nc, cn ng ng hyrxit kali

hp thu kh CO2. Hai ng ny c cn chnh xc t trc v sau khi th nghim. Hiu s

14gia hai ln cn s cho bit khi lng nc v kh CO2 c to thnh, t c th tnh ra

c hyr v cacbon. Ngy nay ngi ta dng my xc nh nguyn t ca Libis-Pregli.

O2

hp th H2Ohp th CO2

cha NO

hp th CO2 v H2O

mu cht

ngng t H2O

My phn tch nguyn t Libis-Pregli

chuyn NO thnh HNO3, cn cho vo bnh cha KMnO4 v H2SO4 m c. Ta cng

c th dng my phn tch ny nh lng halogen.

nh lng nit c th dng cc phng php sau y:

a. Phng php Dumas-Pregli: trong phng php ny, ngi ta t chy hon ton mt

cht hu c c cn chnh xc vi CuO d trong mt dng kh cacbonic. xt nit to

thnh c kh bng Cu kim loi v N2 gii phng c dn vo nit k xc nh th tch.

Bit th tch kh nit, p sut v nhit ca kh c th tnh c lng nit ca hp cht.

b. Phng php Kien-an (Kjeldahl): Mt cht hu c c cn chnh xc, c un

vi axit sunfuric m c c mt t mui thu ngn lm xc tc. Trong phn ng ny nit s

chuyn ho thnh mui amni sunfat, sau un vi dung dch kim mnh s gii phng NH3.

Cho NH3 vo mt lng axit d c chun . Sau khi nh lng phn axit d khng b

trung ho bi NH3 s tnh ra c lng NH3 t suy ra khi lng nit.

(C, H, N) H2SO4 () (NH4)2SO4

HO- NH3

++

+ + . . .(NH4)2SO4

. . .

c. nh lng xy: xy kh nh lng trc tip nn thng ngi ta nh lng cc

nguyn t khc trc ri ly hiu s gia 100% vi tng s phn trm ca cc nguyn t tm

thy.

1.3.3. Xc nh phn t lng.

C nhiu cch khc nhau xc nh phn t lng ca hp cht nhng thng hay dng

t khi hi ca cht hu c cn xc nh so vi khng kh:

M= 29D (D- t khi hi ca cht hu c so vi khng kh)

15Ngi ta cng thng dng phng php khi lng ring ca Dumas bng cch o th

tch ca mt lng kh bit trc mt nhit v p sut xc nh, t c th tnh ra

phn t lng ca n.

1.3.4. Lp cng thc phn t.

lp cng thc phn t ca mt hp cht hu c thng phi:

1. Tnh khi lng cc nguyn t ra phn trm.

2. Chia thnh phn phn trm cc nguyn t cho khi lng nguyn t ca chng bit

s nguyn t gam ca mi nguyn t.

3. Thit lp t l s lng cc nguyn t ca cc nguyn t bng cch chia cho s nh

nht.

4. Lp cng thc phn t n gin.

5. Lp cng thc ng ca phn t bng cch i chiu vi phn t lng ca n.

1.4. CU TRC PHN T CA HP CHT HU C

1.4.1. ng phn cu to.

Nu hai hoc nhiu hp cht khc nhau c cng cng thc phn t nhng c mt s tnh

cht vt l hoc ho hc khc nhau th ngi ta gi chng l cc hp cht ng phn ca nhau.

ng phn cu to l loi ng phn m trong cu to ca chng c s khc nhau v

th t lin kt gia cc nguyn t vi nhau. Ngi ta cn gi ng phn ny l ng phn lin

kt.

V d: Hp cht hyrcacbon C4H10 c th tn ti di hai dng ng phn cu to sau

y:

H C

H

H

C

H

H

C C

H

H

H

H

H H C

H

H

C

H

C

C

H

H

H

HH

H

v

Hyrcacbon C5H12 tn ti di 3 dng ng phn cu to:

H C

H

H

C

H

H

C C

H

H

H

H

C

H

H

H

H C

H

H

C

H

H

C

H

CH3

C

H

H

H

H C

H

H

C

CH3

CH3

C

H

H

H

Khi s lng ca nguyn t cacbon trong phn t hyrcacbon tng ln th s lng cc

ng phn cu to tng rt nhanh. V d C6 c 5 ng phn, C7-9, C8-18, C20-366 319, C40-

62.491.178.805.831 ng phn.

16 Mt loi ng phn cu to khc xut hin khi phn t ca cc hp cht hyrcacbon c

cha cc lin kt bi. V d hp cht hyrcacbon C4H8 tn ti di 2 dng ng phn sau:

H C

H

H

C

H

H

C C

H H

H H C C C C H

H

H

H H H

H

v

1.4.2. ng phn lp th.

ng phn lp th l nhng hp cht c cng thnh phn cu to nhng khc nhau v s

phn b khng gian ca cc nguyn t hoc nhm nguyn t trong phn t. Hin nay ngi ta

chia ng phn lp th thnh 3 loi: ng phn quang hc,ng phn hnh hc, ng phn cu

dng da vo c im cu trc khng gian cng nh cc tnh cht l ho khc nhau ca chng.

1.4.2.1. ng phn quang hc.

ng phn quang hc l nhng hp cht c mt hay nhiu trung tm vt (cacbon bt i

xng, mt phn ca phn t) khng trng vi nh. C hai loi ng phn quang hc l ng

phn quang hc i quang v ng phn quang hc khng i quang.

a. ng phn quang hc i quang: ng phn quang hc i quang l 2 cht c thnh

phn ging nhau, ch khc nhau mt tnh cht l mt phng phn cc ca nh sng phn cc

quay i nhng gc c tr s ging nhau nhng ngc chiu nhau (chiu quay sang phi c k

hiu bng du +, chiu quay sang tri bng du -) v 2 ng phn nh vy vi nhau to thnh

mt cp i quang.

Trng hp trung tm bt i l nguyn t cacbon bt i xng (k hiu l *C) - tc l

nguyn t cacbon lin kt vi 4 nhm th hon ton khc nhau. Mt phn t c cha mt

nguyn t *C c th tn ti di 2 dng ng phn: 1 quay phi v 1 quay tri i xng vi

nhau nh vt v nh qua gng nhng khng th chng kht ln nhau c, tng t nh 2

chic giy ca mt i giy hoc bn tay phi v bn tay tri. V d m hnh t din ca axit (-)-

lactic v (+)-lactic sau y:

COOH

OH CH3

COOH

HOCH3

H H

mt phng gng Cp i quang trn y ca axit lactic c biu din bng m hnh khng gian nhng

i vi nhng phn t phc tp th s dng phng php ny khng thun tin. V vy Fish

17 ngh mt phng php biu din khng gian ca cc ng phn quang hc trn mt phng

gi l cng thc chiu Fish. c cng thc chiu Fish, ta t m hnh t din ca phn t

sao cho nguyn t cacbon bt i xng nm trong mt phng giy, cc lin kt *C-b v *C- c

nm trong mt phng nm ngang hng t mt phng giy n ngi quan st. Cc lin kt *C-

a v *C- d nm trong mt phng thng ng hng ra xa ngi quan st.

a

cb

db c

d

aa

M hnh t din ca *Cabcd Cng thc chiu Fish ca *Cabcd

Chiu cc lin kt xung mt phng giy, ta s c cng thc chiu Fish. Axit lactic trn

y c biu din di dng cng thc chiu Fish nh sau:

COOH

OHH

CH3

COOH

HHO

CH3 i vi mt cht quang hot, ngi ta thng dng quay cc ring [] c trng

cho n. [] c th c gi tr m hoc dng khc nhau ty theo cht quang hot lm quay mt phng ca nh sang phn cc v bn phi hoc bn tri.

b. ng phn quang hc khng i quang: ng phn quang hc khng i quang l

nhng ng phn lp th ca nhau theo ngha chung nhng chng khng phi l nhng ng

phn vt-nh ca nhau. ng phn quang hc khng i quang c th xut hin trong mt s

trng hp sau:

1. Cc t hp bt k ca mt dng i quang ca cp i quang ny vi cc dng i

quang ca nhng cp i quang kia (trng hp ca cc hp cht c t hai cp i quang tr

ln). V d 3-phenylbutanol-2 c ng phn I v II l mt cp i quang, III v IV l mt cp

i quang khc. Cn cc t hp ca I vi III hoc IV, II vi III hoc V l nhng ng phn

quang hc khng i quang ca nhau.

18

CH3OHH

C6H5H

CH3

CH3HHO

HH5C6CH3

CH3OHH

HH5C6CH3

CH3HHO

C6H5H

CH3[ ] = -0,69 [ ] = +30,9 [ ] = -30,2 [ ] = +0,68

2. Cc ng phn mz: Chng l nhng ng phn lp th m phn t ca chng c

cha 2 hoc nhiu trung tm bt i xng nhng gia hai na ca chng c s i xng vt-

nh, do quay cc ca chng b trit tiu khin cho ng phn mz khng quang hot. V

d axit tactric cha hai nguyn t *C (ging nhau) c mt cp i quang v mt ng phn

mz c biu din bng cng thc chiu Fish nh sau:

COOH

HHO

OHH

COOH

COOH

OHH

HHO

COOH

COOH

OHH

OHH

COOH

Cp i quang ng phn mz c. Bin th Raxmic: Bin th Raxmic l hn hp gm cc lng bng nhau ca ng

phn quay phi v ng phn quay tri. N c quay cc ring bng 0 v c k hiu l (). 1.4.2.2. ng phn hnh hc.

ng phn hnh hc l ng phn lp th gy nn bi s phn b khng gian khc nhau

ca nguyn t hay nhm nguyn t xung quanh phn cng nhc ca phn t. Phn cng nhc

c th l mt ni i, 1vng hoc 1 phn vng trong xyclankan

1. Trng hp phn cng nhc trong phn t l mt ni i ta c cc loi ng phn:

a. ng phn cis-trans xut hin cc ni i C-C khi c hai nguyn t hoc nhm

nguyn t nm cng pha hoc khc pha ca mt phng .

CCb b

a aCC

b a

ba

ng phn cis ng phn trans V d: 1, 2-icloten c 2 ng phn sau y:

19

C C

Cl

H

Cl

HC C

Cl

H Cl

H

cis-icloten trans-icloten ng phn syn-anti cng l ng phn cis-trans nhng chng c xut hin cc

hp cht c ni i gia nguyn t cacbon vi mt nguyn t d t hoc gia cc d t vi nhau.

C N

H5C6

H

CH3N N

H5C6 C6H5N N

H5C6

C6H5C N

H5C6

H CH3 syn antisyn anti b. Trng hp phn cng nhc ca phn t l mt ni n hoc mt phn vng trong cc

hp cht vng. V d: axt mtylxyclppanic c ng phn cis v trans nh sau:

HH

COOHCH3

HCH

COOHH

3cis trans Tng t nh vy hp cht 1, 3-imtylxyclhexan c 2 ng phn:

CH

CH3

3CH CH33 cis trans

1.4.2.3. ng phn cu dng.

ng phn cu dng l ng phn lp th ng ca cc phn t hu c c phn bit

nhau bi s phn b khng gian ca cc nguyn t hoc nhm nguyn t trong cng mt cu

hnh. S chuyn ho tng h gia cc ng phn cu dng c thc hin bi s quay quanh

cc lin kt n hoc s b gp ca cc phn vng.

ng phn cu dng quay xut hin cc hp cht mch h khi c s quay ca cc

nguyn t xung quanh trc ca mt hay nhiu lin kt n m khng lm t lin kt ny.

biu din cc ng phn cu dng, ngi ta thng dng cng thc phi cnh, hoc cng thc

chiu Niumen.

Theo cch biu din phi cnh, lin kt gia hai nguyn t cacbon hng theo ng

cho t tri qua phi, ng k vch dng ch cc lin kt nm trong mt phng giy, ng

gch song song nhn dn ch cc lien kt hng v pha di mt phng giy, ng m hnh

tam gic ch cc lin kt hng v pha trn mt phng giy.

20

a

bc

a

b

a

b

c

a

b

d d

Trong cng thc chiu Niumen, phn t c nhn dc theo lin kt C-C (ngha l trc

lin kt ny trc giao vi mt phng giy).

a

bca

bd

Nh vy hai nguyn t ny hon ton che khut nhau v ngi ta biu din chng bng

mt vng trn chung (thc t l hai vng trn chng kht ln nhau). Cc lin kt v cc nhm

th ni vi cc nguyn t cacbon c chiu ln mt phng vung gc vi trc ni hai nguyn

t cacbon (mt phng giy). phn bit hai h thng cc lin kt ni vi cc nguyn t cacbon

th nht v th hai, ngi ta ko di cc lin kt ca cc nhm th vi cc nguyn t cacbon

gn n tm ca ng trn, cn cc lin kt ca cc nguyn t vi nguyn t cacbon xa th

ch gp ng trn m thi.

V d: tan hai nhm mtyl c th quay xung quanh lin kt n C-C khin cho phn t

c th c v s cu dng khc nhau trong c hai cu dng ti hn. Mt cu dng c th nng

cao nht ng vi gc quay ca nhm mtyl l 1200, 2400, 3600 gi l cu dng che khut II,

IV, VI (th nng cao nht do 3 cp hyr i din nhau nht v gn nhau nht nn y nhau

mnh nht), v mt cu dng c th nng thp nht ng vi cc gc quay ca nhm mtyl l

600, 1800 v 3000 gi l cu dng xen k I, III, V (c th nng thp nht do 3 cp hyr nm v

tr cch xa nhau nht nn y nhau yu nht).

H H

H H

H H

H

H

HH

H

H H

H

HH

H

HH

H

H H

H

H

HH

H H

H

H

HH

H H

H H

I II III IV V VI S bin i th nng khi nhm mtyl quay mt vng t 0 n 3600 c biu din trn

gin sau (phn t mtan tri qua 3 cu dng che khut khng khc bit nhau v 3 cu dng

xen k ng nht nhau hng ro th nng lp li 3 ln). Nh vy cu dng xen k c th nng

thp nht nn l dng bn nht. Trng hp mtan dy cc cu dng I, III, V c th nng thp

nht do chng bn nht, dy cc cu dng II, IV, VI c th nng cao nht nn t bn nht.

21

300 360

I

II

III

IV

V

VI

60 120 180 240

E(Kcal/mol)

gc quay o

Gin nng lng ca tan 1.5. LIN KT HO HC.

1.5.1. Cc loi lin kt ho hc.

S pht trin ca l thuyt v lin kt ho hc - tc l lc gi cc nguyn t li vi nhau

trong phn t c chia lm hai thi k: thi trc nm 1926 v t cho n nay. Nm 1926,

nh bc hc Kosen a ra thuyt lin kt ion v nh bc hc Luit a ra thuyt lin kt

cng ho tr. Ni dung ca hai l thuyt c th tm tt nh sau:

Trong nguyn t ht nhn mang in tch dng c bao quanh bi cc in t phn b

thnh cc lp khc nhau. Trn mi lp c s in t nht nh: 2 in t trn lp th nht, 8

in t trn lp th hai, 8 hoc 18 trn lp th 3S to thnh hp cht l kt qu to thnh

lp in t bo ho (ging kh tr) ca cc nguyn t trong phn t. Lin kt ion xut hin do

kt qu ca s chuyn dch electron. V:d qu trnh to thnh hp cht LiF.

Li Li+-e Li + eLi+

F F-+e F + e F-

Do lc ht tnh in dn n to thnh LiF.

Lin kt cng ho tr c hnh thnh bng i in t gp chung. V d: s to thnh

phn t hyr, mi nguyn t hyr c 1 in t nn khi to thnh phn t 2 nguyn t gp

chung cc in t li lm y lp in t cho nhau.

+H H H HTng t: + F FF F

H + H FF

221.5.2. Thuyt c hc lng t.

Nm 1926, nh bc hc Schrodinger a ra thuyt c hc lng t c biu din

di dng mt phng trnh ton hc v s ph thuc ca s chuyn ng ca cc in t vo

nng lng ca n. Phng trnh ny gi l phng trnh sng (electron khng nhng mang

tnh cht ht m cn mang tnh cht sng). Phng tnh sng rt phc tp khng th cho kt qu

chnh xc nn phi dng phng trnh gn ng gi l hm s sng. Hm sng no cho gi tr

nng lng cng thp hm sng cng ng. Tuy mang tnh cht gn ng song thuyt c hc

lng t gii thch c nhiu hin tng c bit l s to thnh phn t v nguyn t.

1.5.3. Ocbitan nguyn t.

Phng trnh sng khng cho php xc nh chnh xc v tr ca in t trong mt thi

im nht nh, tc v qu o chuyn ng ca n nhng cho php xc nh xc sut tm

thy in t mt thi im xc nh. n v khng gian m xc sut tm thy in t l

ln nht gi l ocbitan. C nhiu ocbotan sp xp xung quanh ht nhn khc nhau, c hnh dng

v kch thc khc nhau. Dng ocbitan ca in t c xc nh bi nng lng ca n.

thun tin ngi ta biu din in t di dng cc m my (ging nh tm nh b m). Hnh

dng ca m my chnh l hnh dng ca ocbitan. Cc m my ny khng ng nht. Ocbitan

c nng lng thp nht l 1s-ocbitan.

1s-obitan Ocbitan khng c gii hn xc nh v xc sut tm thy in t rt xa ht nhn vn

c. Trong gii hn biu din hnh trn c ngha l xc sut tm in t l 95%.

Tip theo 1s-ocbitan l 2s-ocbitan c mc nng lng cao hn do lc lin kt tnh in

gia ht nhn v electron yu hn. Cc ocbitan tip theo l 3s-ocbitan, 2p-ocbitan: Px, Py, Pz

23

2px

x

2py

y

2pz

z

Cc ocbitan 2p S phn b in t trn cc ocbitan tun theo nhiu nguyn l khc nhau, c bit

nguyn l ngoi tr Pauli c ngha rt ln. Theo nguyn l ny trn mt ocbitan xc nh ch

c th c ti a l 2 electron vi iu kin chng c s lng t spin i nhau.

I.5.4. Ocbitan nguyn t.

Trong phn t cng nh trong cc nguyn t ring bit cc electron chim cc ocbitan

tng ng vi cc quy tc phn b chng, ch khc ocbitan phn t c nhiu ht nhn. s

dng phng trnh sng trn y cho ocbitan phn t ngi ta a ra 2 iu cho php:

a. Mi mt cp in t ch nh v (gii hn) xung quanh hai ht nhn nguyn t

b. Dng cc ocbitan ca cc electron nh v v s sp xp ca chng ph thuc vo

dng v s sp xp cc ocbitan nguyn t to nn phn t

I.5.5. Lin kt cng ho tr.

to lin kt cng ho tr ocbitan ca nguyn t ny phi xen ph ocbitan ca nguyn

t kia v mi mt ocbitan phi c 1 electron. y xy ra s phi hp 2 ocbitan nguyn t to

thnh mt ocbitan lin kt. Hai electron trn ocbitan lin kt phi c s lng t spin i nhau.

Mi mt nguyn t nm trn ocbitan lin kt chung ny cng c xem nh chng thuc v ca

c hai ht nhn nguyn t. V d s to thnh phn t H2 t 2 nguyn t hiro. y mi

nguyn t hiro c mt electron chim mt ocbitan 1s. to thnh lin kt 2 ht nhn nguyn

t phi tin ti gn nhau sao cho cc ocbitan nguyn t xen ph nhau. Phn t H2 bn vng nht

l khi khong cch gia 2 ht nhn nguyn t l 0,74A0. Khong cch ny c gi l di

kin kt.

H HHHH H

1s 1s ocbitan lin kt Ti khong cch r = 0,74 A0 t hp nng lng ca s xen ph cc electron ca phn t

hyr v s y nhau gia cc ht nhn nguyn t l nh nht.

24(eV )

(Ao )

S ph thu c ca n ng lng in t tro ng ph n t H v o kho ng c ch h a i h t nh n2

1.5.6. Cc phng php tnh gn ng trong lin kt cng ho tr.

gii phng trnh sng cho phn t ngi ta a ra hai phng php gii gn ng.

(1)-Khi xa lc ht gia cc phn t mang in tch tri du l ch yu, khi gn lc y l

ch yu.

(2)-Lun lun y nhau nn khng th to thnh lin kt bn vng c.

a. Phng php s ho tr

Trong phng php ny cc electron c spin i nhau ca hai nguyn t khc nhau A v

B c th ghp i li to thnh lin kt cng ho tr lng electron. Khi to thnh lin kt gia

A v B, ta khng th phn bit c electron I ca A vi electron II ca B. m t iu

ngi ta thng dng cng thc gii hn.

V d:

A c ( AI) v A ( AII)

B c ( BI) v B ( BII)AIBII v AIIBI

(1) (2)

Theo cng thc ny trng thi thc ca phn t phi l ci g trung gian gia (1) v

(2). Do ta c:

1 = IA. IIB v 2 = IIA. IB - l hm sng ocbitan nguyn t . Phng trnh thc ca ocbitan nguyn t s l:

= C11 + C22 Phng php s ho tr dng lm c s ton hc cho quan nim v s cu to cng

hng cc cu to. V d benzen c th biu din bng hai cng thc I v II ca Kkul v ba

cng thc III, IV, V ca ioa.

I II III IV V

25Do phng trnh thc ca benzen s l:

= C1(1 + 2) + C2(III + IV + V) Cc h s C1, C2 c gi tr sao cho nng lng ng vi hm s l cc tiu.

b. Phng php ocbitan.

Phng php ocbitan dng hm sng ca tng electron trong trng bao gm cc ht

nhn v electron cn li.

= C1 1 + C2 2 + .+ C3 3 = Ci I Xt lin kt ho hc theo phng php ocbitan phn t thc cht l m t s phn b

electron trong phn t theo ocbitan ca n theo cc nguyn l cho nguyn t ch khc l ocbitan

nguyn t c nhiu trung tm ht nhn. V d ocbitan nguyn t hyr c hai trung tm ht

nhn. Trong trng hp ny nghim ca phng trnh sng gii ra phi c hai nghim ng vi

nhng trng thi khc nhau ca phn t. Trng thi th nht ng vi s ht nhau c nng lng

thp hn nng lng ca nguyn t l trng thi ocbitan phn t lin kt:

lk = C1 1 + C2 2 ocbitan lin kt mt gp electron gia hai ht nhn l ln nht, tri li ocbitan

phn lin kt l bng 0.

HH +-

+H H

obitan lin kt

obitan phn lin kt

obitan lin kt

obitan phn lin kt

H1s

H1s

+

i vi nhng h c nhiu trung tm v nhiu electron vic gii phng trnh sng s

dn n nhiu nghim ng vi nhng trng thi nng lng khc nhau.

1.5.7. S xen ph v s lai ho.

a. S xen ph.

Lin kt cng ho tr c hnh thnh l do s xen ph ca cc ocbitan nguyn t thnh

cc ocbitan phn t lin kt. Ocbitan phn t lin kt cng bn v nng lng thot ra khi hnh

thnh ocbitan cng ln nu vng xen ph ocbitan cng ln. Khuynh hng ca s xen

ph l tin ti cc i. Mun cho cc ocbitan nguyn t tng tc c hiu lc vi nhau thnh

ocbitan phn t chng phi tho mn 3 iu kin sau y:

1- Nng lng ca chng gn bng nhau.

2- S xen ph mc ln.

3- Chng phi c cng mt kiu i xng vi trc ni hai nhn nguyn t.

26Xt iu kin 3 ta c th xen ph:

- Hai ocbitan s

- Mt ocbitan s vi mt ocbitan p no c trc i xng trng vi trc ni hai ht

nhn.

- Hai ocbitan p c trc i xng song song vi nhau (cng px, py hoc pz)

S xen ph c th theo trc hay bn trc ni gia hai ht nhn nguyn t.

Theo trc:

*

+- +

- + -

+-+

sp

Ocbitan lin kt c trc i xng l ng thng ni gia hai ht nhn v c gi l

ocbitan . Lin kt cng ho tr c hnh thnh gi l lin kt . S xen ph xy ra tng t nh vy i vi trng hp ocbitan p + p.

+- +-

- + - +

+-+-

*

p p

S xen ph bn trc:

II

+

-

+

-

+

-

-

+

+

-

+

p pII

II*

S xen ph bn trc s to thnh ocbitan v lin kt . V ocbitan khng c tnh i xng i vi trc hai ht nhn m ch i xng vi mt

phng nt cha 2 trc nn lin kt t bn, d phn cc ho. Mt khc cn tr s quay t do ca nguyn t hay nhm nguyn t xung quanh trc lin kt (do s quay s vi phm nguyn

l cc i). l nguyn nhn lm xut hin cc ng phn hnh hc.

b. S lai ho.

27Ph hp vi nguyn l xen ph cc i, tng hiu lc ca s lin kt, cc ocbitan

tham gia xen ph c th b lai ho. Ni dung ca s lai ho c th tm tt trong trng hp hnh

thnh CH4 nh sau:

Cacbon C6 -1s22s22p2

s21 p22s22

Theo s ho tr trn y th ccbon c ho tr 2 do nu kt hp vi nguyn t hyr

th phi to thnh hp cht CH2. Th nhng trong phn t mtan, cacbon c ho tr 4. iu

c gii thch rng: c mt electron ca ocbitan 2s chuyn qua ocbitan p cn trng.

s21 p32s12

Kt qu to thnh 4 in t c thn v do c th hp vi 4 nguyn t hyr to thnh

CH4. Nh vy c th nhn thy rng cacbon s to thnh 3 lin kt c cng mt loi lin kt ca

cc ocbitan p v mt lin kt ca ocbitan s. Nhng thc t 4 lin kt ca CH4 hon ton ging

nhau. iu c gii thch bi s lai ho ca cc ocbitan-tc l s t hp lai to thnh nhng

ocbitan c dng khc vi ocbitan ban u c kh nng xen ph cao hn do lin kt hnh

thnh bn vng hn. Thc vy cc kt qu tnh ton cho thy rng:

1- Ocbitan lai to tt nht c hng xen ph cao hn ocbitan s hoc ocbitan p.

2- 4 ocbitan lai to tt nht c hng xen ph cao hn hon ton ng nht vi nhau.

3- Cc ocbitan ny hng n gc ca mt t din u- tc l s sp xp m trong

cc ocbitan nm v tr cch xa nhau nht. S lai ho ny gi l lai ho t din. Gc

lai ho trong trng hp ny l 109028.

lai ha sp3

s21 sp3

s21 p32s12

S lai ho sp3 c th biu din nh sau:

+

1 3 2s p sp3

28

x

y

z s + 3p sp3

lai ha

Cc kt qu tnh ton cho thy rng nu coi kh nng xen ph ca ocbitan s l 1 th

ocbitan p l 3 v ocbitan lai ho sp3 l 2. Trong phn t mtan cng nh cc ng ng ca n, ocbitan lai to sp3 ca cacbon xen ph vi ocbitan 1s ca hyr to thnh lin kt (C-H). cc ng ng ca mtan 2 ocbitan sp3 ca hai nguyn t cacbon bn cnh nhau to thnh lin

kt (C-C). V gc ho tr ca nguyn t cacbon sp3 l 109028 nn mch cacbon trong phn t ankan l ng gp khc khc hnh ziczc.

H

HH

HH

H HH

H

H

HH

H

H

HH

H

H

H

H

CH CH CH CH CH CH CH4 33 3 2 2 3 Kiu lai ho th hai l s tng hp 1 ocbitan s vi 2 ocbitan p to thnh 3 ocbitan sp2 (lai

to tam gic hoc lai ho phng). Trc i xng ca 3 ocbitan sp2 nm trn mt mt phng to

thnh gc 1200. Kh nng xen ph tng i ca ocbitan sp2 l 1,99.

x

y+

++

s + 2p sp2

lai ha sp2

s21 sp2 p12

s21 p32s12

Trong phn t tylen cc ocbitan sp2 tham gia xen ph to nn 5 lin kt c trc nm

trong mt mt phng. Cn li 2 ocbitan p thun khit cha lai to xen ph bn nhau to thnh

lin kt .

29

H

H

H

H

C CH

H

H

H

Kiu lai ha sp-t hp ca mt ocbitan s v mt ocbitan p gp trong cc phn t c ni 3

vi kh nng xen ph l 1,93 v gc to bi trc i xng ca 2 ocbitan l 1800 (kiu lai ho

ng thng).

+ +- + - +-sps + p

lai ha sp

s21 p32s12

s21 sp p22 Trong phn t axtylen, cc ocbitan lai ho sp xen ph ln nhau v vi ocbitan hyr

(1s) to thnh 3 lin kt m trc lin kt cng nm trn mt \ng thng, cn li 4 ocbitan p thun khit chng s xen ph bn nhau tng i mt to nn 2 lin kt .

Cc lin kt ca axtylen. H C C H

H H C C CH C H

1.5.8. Mt s c tnh ca lin kt cng ho tr .

a. Nng lng lin kt.

Nng lng lin kt A-B l s nng lng thot ra khi hnh thnh lin kt t hai

nguyn t A v B hay hai gc t do A. v B.. cng chnh l nng lng cn thit lm t

lin kt A-B thnh 2 nguyn t hoc 2 gc t do. Tuy vy nng lng lin kt ch nhng gi tr

trung bnh gn ng ca nng lng phn ly. V d khi dng khi nim nng lng lin kt ta

gi thit rng tt c cc lin kt C-H chng hn trong ankan l nh nhau. Thc ra nng lng

30cn thit lm t lin kt C-H th nht trong mtan chng hn khng phi bng nng

lng cn thit phn cp hon ton phn t ny thnh cacbon v hyr, cng khng phi

bng nng lng lm t C-H trong tan, prpan, bezenNng lng lin kt ca C=C v CC khng ln gp i hay gp ba ca C-C.

b. S phn cc.

Trong lin kt cng ho tr cp electron lin kt hay ocbitan phn t lin kt ch c

phn b tht u gia hai nguyn t v mmen lng cc bng 0 khi no hai nguyn t hon

ton ng nht nh h A-A: Cl-Cl, H-H, H3C-CH3Trong trng hp hai nguyn t lin kt

vi nhau khng ng nht h A-B: H-Cl, CH3-Clcp electron lin kt s lch i t nhiu v

pha mt nguyn t no c m in ln hn v do lin kt c mmen lng cc khc 0

( 0).

A BA AA B

H A-A H A-B

HA=B

A B S phn cc khng nhng c th xy ra lin kt m cn xy ra c lin kt , h

A=B hoc AB, v d H2C=O, -CN m t s phn cc ca lin kt cng ho tr ngi ta thng dng mi tn thng cho

lin kt v mi tn cong cho lin kt (chiu mi tn l chiu chuyn dch ca cc electron).

H3C Cl H3C Cl+ -

hoc hoc H3C Cl+ -

hocH2C O H2C O- + + - H2C Ohoc

1.6. L THUYT V S CHUYN DCH ELECTRON TRONG PHN T CC

HP CHT HU C.

1.6.1. Hiu ng cm ng.

a. nh ngha v phn loi.

Xt hai phn t prpan v n-prpylclorua.

H C C C H

H

H

H

H

H

H

H C3

H

H

C1

H

H

C2

H

HCl

+ + +

Khc vi prpan, prpylclorua c nguyn t clo vi m in ln do lin kt C1-Cl

b phn cc v kt qu clo mang mt phn in tch m v CI mang mt phn in tch dng.

V C1 c mt in tch dng nh nn lin kt C1-C2 b phn cc v pha C1, n lt C3-C2

31li cng b phn cc v pha C2. S phn cc khng nhng xy ra lin kt C-C m cn c

lin kt C-H. Kt qu l phn t b phn cc v xut hin mt mmen lng cc, cn hyr th

tr nn linh ng hn (so vi hyr prpan). Dng phn cc ny gi l phn cc cm ng hay

hiu ng cm ng.

Vy bn cht ca vn hiu ng cm ng l s phn cc cc lin kt lan truyn theo

mch cc lin kt do s khc nhau v m in. Ngi ta k hiu hiu ng cm ng I

(Inductive Effect). Hiu ng cm ng c th gy ra bi nguyn t hay nhm nguyn t ht

electron gi l hiu ng cm ng m (-I), nguyn t hay nhm nguyn t nhng electron gi l

hiu ng cm ng dng (+I). Chiu chuyn dch electron c m t bng mi tn.

Y C C H C X(+I) (I=0) (-I)

b. Quy lut v hiu ng cm ng ca nguyn t v nhm nguyn t.

Phn tch nhng d kin v hiu ng cm ng nhng nguyn t hay nhm nguyn t

khc nhau ngi ta rt ra mt s quy lut sau:

1. Cc nhm mang in tch dng c hiu ng -I, cc nhm mang in tch m c hiu

ng +I. V d: -N+R3 l nhm I mnh cn O- l nhm +I mnh.

2. Nu cc nguyn t ca cng cc nguyn t cng mt chu k nh hay phn nhm

chnh trong h thng tun hon u c hiu ng I th hiu ng cng ln khi nguyn t tng

ng cng v pha bn phi chu k hoc cng pha trn phn nhm chnh.

F > Cl > Br > I

F > OR > NR2

3. Cc nhm ankyl lun lun c hiu ng +I, hiu ng tng theo bc ca nhm:

CH3 < CH3CH2 < CH(CH3)2 < C(CH3)3

4. Trng thi lai to ca cacbon c I bin i:

Csp > Csp2 > Csp3 tc l RCC- > C6H5- > R2C=CR- c. c im ca hiu ng cm ng.

c im ni bt ca hiu ng cm ng I l gim rt nhanh khi ko di mch truyn nh

hng.V d nh hng ca clo n lc ca axt butyric nh sau:

Ka.105 1,5 3,0 8,9 139,0

CH3CH2CH2COOH CHCOOH

CH2CH3

Cl

CHCH2COOH

CH3

Cl

Cl CH2CH2CH2COOH

Theo kt qu ca bng trn y th clo v tr lm tng lc axit ln 87 ln, v tr

lm tng 6 ln, v tr lm tng 2 ln.

321.6.2. Hiu ng lin hp.

a. nh ngha v phn loi.

xt hiu ng lin hp ta xt phn t n gin c h cc lin kt lin hp l butaien.

Tng t nh trong phn t tylen, cc nguyn t cacbon trong phn t butaien u trng

thi lai ho sp2 v h thng cc lin kt l mt h phng. Mi nguyn t cacbon cn li mt ocbitan p thun khit xen ph vi nhau to thnh 4 ocbitan phn t khc nhau I, II, III, IV. Cc tnh ton c lng t cho thy rng ocbitan phn t IV c nng lng thp nht ( bao trm c 4 nguyn t cacbon gi l ocbitan gii to hay khng khu tr). H phn t c ocbitan gii to

nh butaien gi l h lin hp. H lin hp thng gp , p v , V d:

C C C C

CH2 CH CH CH2

H mch h ,

H lin hp , pC C X

CH2 C Cl

H mch vng ,

I

II

III

IV

Bnh thng phn t butaien c gii ta nh IV. Nu thay mt nguyn t hyr CH2

bng CH=O chng hn th do c tnh phn cc sn c ca nhm CHO s lm cho mt

electron chuyn ng dch mt phn v pha n lm cho ton b phn t b phn cc.

CH2 CH CH CH2 CH2 CH CH CH CH O

Ta ni y c hiu ng lin hp v nhm CHO gy hiu ng lin hp (k hiu l C).

Nhm CHO lm chuyn dch mt electron v pha n nn c hiu ng lin hp m (-C).

Ngc li, nu nguyn t hay nhm nguyn t lm mt electron chuyn dch t pha n n

cacbon th n c hiu ng lin hp dng (+C).

Vy hiu ng lin hp l hiu ng electron truyn trn h lin hp gy nn s phn cc

h electron trn . b. Quan h gia cu to ca nhm th vi hiu ng lin hp.

Hiu ng lin hp c 3 loi:

1. Cc nhm +C: Cc nhm ny ni chung u c cp electron cha s dng hay

electron d:

33-O-, -S-, -OH, -SH, -NH2, -NR2, -NHCOCH3, -F, -Cl, -Br.

ng ch l hu ht cc nhm c hiu ng +C ng thi c hiu ng I mc khc

nhau. V vy trong trng hp c th cn phn bit nh hng ca mi loi. V d: CH3O- l

nhm y electron ni chung v c khi ni ring v nh hng lin hp v +C > -I.

CH CH CH CH2CH3O+C

-I Tri li clo l nhm ht electron ni chung v +C< -I.

CH2 CH CH CH Cl-I

+C

i vi cc nguyn t hay nhm nguyn t c cng hiu ng lin hp +C th: nguyn t

mang in m c hiu ng +C mnh hn nguyn t tng t khng mang in.

O- > -OR

-S- > - SR

Trong mt chu k nguyn t cng bn phi th +C cng yu:

-NR2 > -OR > -F

Trong mt phn nhm chnh lc +C gim t trn xung di:

-F > -Cl > -Br > -I

-OR > -SR > -SeR

2. Cc nhm C: a s cc nhm ny l nhng nhm khng no:

-NO2, -CN, -CHO, -COR, -COOH, -CONH2 Thng cc nhm C c c hiu ng I.

Cc nhm -C=Z c lc C ph thuc vo Z ( nu Z cng bn phi chu k th lc C

cng ln):

C O C NR C CR2

Nhm mang in tch dng c C ln hn khng mang in:

C NRC NR2+

3. Cc nhm c hiu ng C vi du khng c nh.

Loi ny thng l nguyn t hoc nhm nguyn t cha no nh: vinyl, phenylV

d: trong phn t nitrbenzen v anilin phenyl, c th biu hin hiu ng +C hay C ty theo

nhm nguyn t gn vi phenyl l -NO2 (nhm C) hay NH2 (nhm +C).

34

O2N

-C +C

H2N

+C -C c im ca hiu ng lin hp: n thay i tng i t khi ko di mch cc lin kt

lin hp. Hiu ng lin hp ch c hiu lc mnh trn h lin hp phng (tc l cc ocbitan p

thun khit phi c trc song song vi nhau).

N N

X

XH , p phng H , p khng phng

1.7. MT S PHNG PHP VT L THNG DNG TRONG HO HC HU

C

xc nh cng thc cu to ca mt hp cht hu c, trong phn trc ta xem xt

cc phng php tinh ch cc hp cht, xc nh thnh phn v khi lng cc nguyn t c

trong mt phn t. Ngy nay xc nh cu to ca mt hp cht hu c nhanh hn v chnh

xc hn, ngi ta dng cc phng php vt l nh khi ph, quang ph hng ngoi, ph cng

hng t ht nhn

1.7.1. Khi ph.

Nu ta bn ph phn t ca mt hp cht hu c bng mt dng electron c nng lng

trung bnh (20-70 electron-vn) th cc phn t s b ion ho v ph v thnh nhiu mnh khc

nhau, trong c mt s mnh l ion dng. T l khi lng ca mi loi ion vi din tch

(m/e) chnh l khi lng ca ion. V d nu ta bn ph phn t nopentan:

C

CH3CH3H3C

CH3 M+(C5H12)+ M1+(C4H9)+ M2+(C3H5)+ M3+(C2H5)+ M4+(C2H3)+

m/e 72 57 41 29 27

Nu cho dng cc ion dng ny vo mt t trng hng vung gc vi hng ca t

trng th cc ion c t l m/e khc nhau nn di tc dng ca t trng s b lch i khi

hng ban u nhng qu o khc nhau. Tn hiu thay i ny ca cc ion s c mt b

phn ghi t ng ghi li v cho ta ph khi lng ca hp cht cn xc nh m trong mi

35loi ion s c th hin bng mt pic ring bit c cng ng vi i lng m/e. Pic c bn

c cng tng i ln nht M+ tng ng vi phn t lng ca phn t. Tuy nhin nhiu

khi pic M+ l mt pic c cng tng i yu. V d khi ph ca nopentan, M+ ng vi

phn t lng ca phn t c cng tng i yu, cn M+ ng vi phn t lng ca

butanhytc cng tng i ln nht.

M+M1+

M2+M3+

M4+

10 20 30 40 50 60 70 80 90 100 110 120 130 140

25

50

75

100

0

I / I0 (%)

Ph khi lng ca nopentan

10 20 30 40 50 60 70 80 90 100 110 120 130 1400

I / I0 (%)

20

40

60

80

100M+ = 72

57(M-CH ) 3 +

43(M-CHO)+

29(CHO)+

15(CH ) 3 +

Ph khi lng ca butanhyt

1.7.2. Quang ph hp ph.

a. Quang ph in t.

Chng ta bit mt s bc x in t nh nh sang thng, nh sng cc tm, hng

ngoi, tia Rngen, sng rai

xa c s

p.quay p.dao ng

gn gn xa

Hng ngoi T ngoi

p.electron

Tia XTia

cm-1 10 103 5.103 104 106

Tt c cc loi sng trn y u c mt tc truyn sng l 3.1010 cm/s v tn s =

c/ trong c l tc truyn sng, l di sng (cm). Khi mt chm tia sng in t gp phi mt vt no th n c th xuyn qua, cng c

th b hp th li ph thuc vo tn s ca sng v cu to ca vt th. Ta bit rng, bc x in

t l mt dng nng lng, do khi phn t hp th bc x in t th n c cung cp

thm mt nng lng E= E1-E0 = h = hc/.

36Nng lng E c phn t hp th, c th gy ra s dao ng, s quay ca cc nguyn

t trong phn t hoc bc chuyn electron n mt mc nng lng cao hn. Tn s bc x

m mt phn t nht nh c th hp thu ph thuc vo trng thi dao ng hay trng thi

quay ca cc nguyn t cu to nn phn t.

Vy ph ca mt hp cht l th cho php xc nh phn no ca bc x in t b hp

th (hay i qua) vt th mt tn s nht nh. N mang tnh cht c trng cho cu to ca

cht.

b. Quang ph hng ngoi.

Trong ho hc hu c, ph hng ngoi c ngha rt ln xc nh cu to ca hp

cht.

Phn t lun lun dao ng. Nu dao ng lm thay i di cc lin kt th ngi ta

ni l dao ng ho tr, cn nu thay i gc lin kt th ngi ta gi l dao ng bin

dng.

Gi s phn t c n nguyn t, vy c 3n bc t do trong 3 bc dng xc nh

chuyn ng tnh tin, 3 bc dng xc nh chuyn ng quay v cn li 3n-6 bc l dao

ng t do (phn t thng hng, c 3n-5 bc dao ng t do v ch c hai bc chuyn ng

quay). V d phn t H2O c n=3 do 3.3-6=3 bc dao ng t do.

a b ca,b - dao ng ha tr c - dao ng bin dng

S thay i dao ng t do ca phn t c gy c gy ra bi s hp th trong vng

hng ngoi. ch ra v tr hp th trong vng ngoi, c th s dng di sng hay tn s

(thng hay dng tn s c biu th bng n v s sng cm-1)

Ph hng ngoi c gi tr xc nh nhng nguyn t hay nhm nguyn t no c

(hoc khng) trong phn t.

Bng tn s hp th ca mt s nhm trong ph hng ngoi.

Lin kt Loi hp cht Tn s cm-1

C-H

C-H

C-H

C-C

Ankan

Anken

Ankin

Anken

2850-2960

3020-3080

3300-3340

1640-1680

37C-C

C-O

O-H

Ankin

Anhyt, xton

Ancol

2100-2260

1690-1760

3610-3640

1.7.3. Ph cng hng t ht nhn (CTN).

Ht ca mt s nguyn t ging nh electron c spin. Theo tnh ton ca c hc lng t

th s spin ca ht nhn nguyn t c th phn thnh:

I=0 12C, 16O, 28Si

I=1/2 1H, 3H, 13C, 19F, 31P

I=1 2H, 14N

I=3/2 1B, 35Cl, 37Cl

I= c nhng gi tr cao hn.

V cc ht nhn nguyn t l nhng phn mang in tch nn nhng ht nhn c I0 khi quay quanh trc ca n s sinh ra mt mmen t . Cc ht nhn c mmen t I=0 khng c tn hiu cng hng t nhn. Cc ht nhn c I>1/2 cho cc tn hiu cng hng t nhn rt phc

tp nn t s dng. Ch c cc ht nhn c I=1/2 thun tin cho CTN. c bit trong ho hc

hu, thng s dng ph cng hng t ht nhn ca proton (CTP) v proton c hu ht trong

cc hp cht hu c.

Nu t proton trong t trng H0, theo nh lut c hc lng t mmen t ca proton

c th c 2I+1 nh hng, tc l 2.1/2 +1 = 2:

- Mt nh hng theo t trng H0 (m= +1/2)

- Mt ng hng i lp vi t trng H0 (m= -1/2)

iu c ngha l proton trong t trng H0 c xp trn 2 mc nng lng: E1= +

.H0 E2= -H0 Nh vy chuyn hng i lp vi t trng theo hng vi t trng cn phi c

mt nng lng E= E1-E2 = 2.H0. Thay = h/4 (trong hng s c trng cho mi ht nhn, h l hng s Plng).

C-H C=C CH3

CH2

C-H

38Ta c: E = hH0/2 (E ch ph thuc vo H0) Mt khc theo nh lut hp th, s cng hng ch xy ra khi:

E = h Suy ra: h= hH0/2 do = H0/2 l tn s m ti xy ra cng hng. Nguyn tc hot ng ca mt my CHP nh sau:

My ghi dao ng

My t ghi

B khuych i

B to sng

A M Hp cht AM

Trong thc t c th thu nhn ph CHP bng hai cch:

1- C nh t trng H0 v lm thay i tn s ca trng in t. 2- C nh tn s v lm thay i H0 (phng php ny thng hay s dng hn). Nu tt c xy ra n gin nh trnh by trn y th tt c mi prton ca cc phn t

ca cc cht hu c u hp th mt H0 nht nh v ph cng hng prton ch c mt vch.

Nhng t c mt cng H0 (cng hiu dng) th do mt in tch bao quanh

cc proton khc nhau nn cn phi tc dng ln mi mt proton mt t trng H (cng tc

dng) khc nhau.

Nh vy mt tn s xc nh cc proton u hp th mt cng hiu dng nh nhau nhng khc nhau v cng tc dng H. Chnh s khc nhau nay cho php thu nhn ph

CHP thnh nhng dy pic hp th c trng cho s bao bc ca cc electron xung quanh

proton.

Ph CHP cho ta thng tin cn thit xc nh cu to ca phn t sau y:

1- S lng cc tn hiu cng hng ch ra c bao nhiu loi proton khc nhau trong

phn t.

I/I0

H

39V d: CH3-CH2-Cl CH3CHCl-CH3 CH3-CH2-CH2-Cl

a b a b a a b c

(2 tn hiu) (2 tn hiu) (3 tn hiu)

2- V tr tn hiu cng hng ch ra thng tin v s bao bc ca electron xung quanh

proton. V tr ny c nh gi bng khong cch gia tn hiu ca nhng nhm ht nhn c

kho st v tn hiu ca cht lm chun. i lng c gi l chuyn dch ho hc.

chuyn dch ho hc c o bng n v phn triu (pt). Cht lm chun thng chn l

ttramtylsilan (TMS) v TMS ch c mt vch hp v vch ny xa cc tn hiu cng hng

prton khc. Hin nay trong ho hc tn ti hai loi thang o o chuyn dch ho hc v lin h vi nhau theo =10 +

Trong v d di y chuyn dch ho hc ca CH3 l 0,9pt; -CH2 l 1,3pt; -CH l

1,5pt c vit nh sau: ph CHP, , pt. 0,9(CH3); 1,3(CH2); 1,5(CH).

3- Cng (din tch ca pic) ch ra s lng ca proton mi loi trong phn t.

Thng cng ny c ch ra trn ph CHP bng ng bc thang v mi bc ca n t l

vi din tch ca tn hiu.V d trong ph CHP ca p-tecbutyltoluen sau y c s lng proton

a l 9 tng ng vi 18mm, proton b l 3 tng ng vi 6mm, proton c l 4 tng ng vi

8mm.

CH

CH2

CH3

TMS

1 2 3 4 0

404- S phn chia tn hiu thnh cc vch ch ra nh hng ca cc proton xung quanh n

proton kho st do s tng tc spin-spin. V d trong ph CHP ca etylbrmua tn hiu cng

hng ca nhm CH3 l 3 vch, cn ca CH2 l 4 vch.

Xt nhm CH3 ta thy proton ca n b nh hng bi nhm CH2. Trong t trng

proton CH2 c th nh hng:

-1/2 + (-1/2) = -1

-1/2 +1/2 -1/2 +1/2 = 0

+1/2 +1/2 = 1H0 Do nh hng ca proton CH2 nh trn nn proton nhm CH3 b phn thnh 3 vch theo

t l 1:2:1.

Xt proton CH2 ta thy n b nh hng ca nhm CH3. Trong t trng ca CH3 n c

th nh hng:

H0

Do nh hng ca nhm CH3 nn proton ca nhm CH2 b phn thnh 4 vch theo t l

1:3:3:1.

Khong cch gia cc vch k nhau ca mt tp hp c o bng Hz gi l hng s

tng tc spin-spin J. Hng s ny c trng cho s tng tc gia cc nhm nguyn t trong

ph CHP.

411.8. PHN LOI CC PHN NG TRONG HO HC HU C.

Cc phn ng hu c phn loi bng nhiu cch khc nhau: theo tin trnh phn ng, theo

phng thc sp xp li lin kt v theo s cc phn t tham gia vo bc quyt nh tc

phn ng.

1.8.1. Theo tin trnh phn ng.

a. Cc phn ng cng hp (k hiu l A t ch addition tc l cng hp).

V d:

C C + Br Br C

Br

C

Br

R NH2 H+ R NH3+

+

b. Cc phn ng tch loi (k hiu l E t ch Elimination tc l tch)

V d:

C

H

C

OHC C + H2O

c. Cc phn ng th (k hiu l S t ch Substitution tc l th).

V d:

R X Y- R Y X-+ +

R H Cl Cl R Cl HCl+ +

1.8.2. Theo phng thc sp xp li lin kt.

a. Cc phn ng gc.

y l loi phn ng m trong mt s giai on ca phn ng xut hin nhng

sn phm (hay sn phm trung gian) c mt in t khng lin kt. Thng cc gc t do c

to thnh do s phn ct ng ly.

V d:

A B A. + B.

Cl Cl 2Cl.

RO OR 2RO. b. Cc phn ng phn cc hay phn ng ion.

Trong nhng phn ng ny cc lin kt c tch ra hay to thnh bng mt cch bt i

xng, tc l cp lin kt c mt bn gi li hoc do mt bn ca lin kt mang . Thng

cp lin kt in t c to thnh do s phn ct d ly.

42V d:

A+ B-+A B

H Cl H+ Cl-+

Ta phn bit nhng phn ng i nhn N (Nucleophin) v nhng phn ng i in t E

(Electronphin). Theo qui nh bao gi cng cn c vo tc nhn phn ng (reagent) xc nh

xem mt phn ng l i nhn hay i in t. Nhng cng ging nh phn ng xi ho- kh i

nhn v i in t l hai mt ca mt qu trnh gn b vi nhau cho nn nhiu khi gi mt cu

t tham gia phn ng l tc nhn hay l hp cht (substrat) ch l iu kin tu . Thng th

cht c cu trc t phc tp l tc nhn, cn cht c cu trc phc tp l cht nn. V d trong

phn ng cng triankylamin vi boriflorua th triankylamin l tc nhn i nhn cn boriflorua l

tc nhn i in t.

NRR

R

B FF

Fi nhn

i in t

NRR

R

B FF

F

Cc tc nhn i nhn thng l:

- Cc ion c in tch m, cc hp cht c cp in t t do, cc hp cht c lin kt bi

hoc cc hp cht thm.

Cc tc nhn i in t thng l:

- Cc ion c in tch dng, cc hp cht c v in t cha hon chnh (Axit Liut), cc

hp cht axtylen, cc hp cht c nhm cacbnyl, cc halogen.

1.8.3 Theo s cc phn t tham gia bc quyt nh tc phn ng.

1, Cc phn ng n phn t

2, Cc phn ng lng phn t

3, Cc phn ng c s phn t cao hn

43CU HI N TP V BI TP CHNG 1

1.1. Bn cht v c im lin kt cng ha tr.

1.2. nh ngha hin tng ng phn lp th, phn loi ng phn lp th

1.3. iu kin cn v c ng phn hnh hc. Cch gi tn cc ng phn hnh hc.

1.4. iu kin cn v c ng phn quang hc. Cch gi tn cc ng phn quang hc.

1.5. Bn cht v c im ca hiu ng cm ng v hiu ng lin hp.

1.6. Vit cng thc cc ng phn hnh hc c th c v gi tn cc ng phn , ng vi cc

cng thc cu to sau: CH3 CH CH2 Cl CH CH Br

CH3 CH CH C2H5 CH3 CH

CH3

CH CCH3

C2H5

a.

b.

c.

d.

1.7. Trong cc hp cht sau, hp cht no c tnh quang hot.

CH3 CH CH3OH

CH3 C

Cl

H

CH2 CH3 CH3 CH

CH3C

H

Br

CH3

CH3 CH

CH3

C

OH

CH3

CH2 CH2 CH3CH3 C

H

CH2 CH2 CH3

CH2 CH2 CH3

a. b. c.

d. e.

1.8. Vit cng thc cc ng phn lp th ca cc hp cht sau y v cho bit loi ng phn.

CH3 CH CH CH CH CH3 CH2 CH CH2 CH2 CH CH2

CH3 CH CH CH3Br Br

C6H5 N N C6H5 CH3 CH CH CH

CH3

COOH

a. b.

c. d. e.

1.9. Trong cc hp cht sau, hp cht no c hiu ng lin hp.

CH2 CH CH CH2CH3 CH C CH2

CH3 CH CH CH O

CH3 C NH2O

CH2 CH CH2 CH CH2a. b.

c. d. e.

1.10. Sp xp cc hp cht sau theo th t tng dn tnh axit.

ClCH2CH2COOH, FCH2CH2COOH, BrCH2CH2COOH

NO2 COOH, COOH, COOHCH3O

a.

b.

44TI LIU THAM KHO CA BI TP CHNG 1

[1]. Chu Phm Ngc Sn, Nguyn Hu Tnh, Nguyn Huy Ngc, L Khc Tch, Bi tp

ha hc hu c.

[2]. Ng th Thun, Bi tp ha hc hu c (2008), Nxb. Khoa hc v K thut, H Ni.

[3]. Thi Don Tnh, Bi tp c s l thuyt ha hu c (2005), Nxb. Khoa hc v K thut,

H Ni.

[4]. Thi Don Tnh, Bi tp c s ha hc hu c (2005), Nxb. Khoa hc v K thut, H

Ni.

[5]. Nguyn th Bch Tuyt (1995), Gio trnh ha hu c, Hu.

45Chng 2

HYRCACBON NO

(ANKAN)

Cc hp cht hu c ch c cha 2 nguyn t hyr v cacbon c gi l hyrcacbon.

Da vo s cu to khc nhau, cc hyrcacbon c chia lm hai loi chnh: hp cht khng

thm v hp cht thm. Cc hp cht khng thm c chia thnh ankan, anken, ankin v cc

hp cht mch vng tng ng ca chng (xyclankan, xyclanken, xiclankin).

2.1. Dy ng ng, ng phn.

Hp cht n gin nht ca ankan l CH4. N c cu to t din (nguyn t cacbon c

ocbitan lai to sp3, gc lin kt l 109028, di lin kt l 1,09 A0).

Cc hp cht tip theo l tan, prpan, butangi l cc hp cht ng ng ca ankan:

CH4, CH3-CH3, CH3-CH2-CH3, CH3-CH2-CH2-CH3

Dy hp cht m trong thnh phn phn t ca hp cht tip theo khc vi thnh phn

phn t ca hp cht trc mt n v cu to nht nh gi l dy ng ng. Cc hp cht

ca dy gi l cht ng ng.

Nh vy cc hp cht ankan to thnh dy ng ng ankan m trong hai hp cht k

nhau khc nhau bi mt n v cu to l CH2. T ta suy ra cng thc tng qut ca ankan

l: CnH2n+2.

Cng vi s tng ln ca s lng nguyn t cacbon trong phn t s lm tng s lng

nhng kh nng phn b khc nhau ca cc nguyn t cacbon dn n s to thnh cc ng

phn khc nhau.

V d: pentan c 3 ng phn, hecxan c 5 ng phn, heptan c 9 ng phn, kan c

75 ng phn, kzan (C20H42) c 366.319 ng phn.

Pentan (C5H12)

C C C C C C C C C

C

C

C

C

C

C

n-pentan izpentan neopentan 2.2. Danh php

Cc hyrcacbon c gi tn thao cc danh php nh trnh by phn i cng

(1.1.5).

2.3. Tnh cht vt l.

Lc lin kt phn t gm 2 loi: lc tc dng lng cc v lc Van-ec-van.

46Lc tc dng lng cc c gy ra bi s ht nhau ca u mang in tch dng ca

phn t phn cc ny vi u m ca phn t kia. (v d nh trong phn t HCl).

+ -

- + Trong trng hp hp cht khng phn cc, s phn b ca in tch l i xng (v d

CH4) do tng cc mmen phn cc bng 0. Nhng mt khc in tch lun lun chuyn

ng, v vy mt thi im xc nh no s phn b ca chng thay i do lm xut

hin mt s phn cc nh. Chnh s phn cc tc thi ny lm nh hng n s phn b ca

cc in t trong phn t CH4 khc. Kt qu lm phn t phn cc cm ng. S phn cc ny

to ra lc lin kt cc phn t li vi nhau. Lc chnh l lc Van-ec-van. Lc ny c hiu

lc trong mt khong cch ngn v ch gia cc phn t tip xc vi nhau, tc l gia cc b

mt ca cc phn t. V vy phn t cng ln, tc l b mt ca cc phn t cng ln th lc

cng mnh. Thc nghim chng minh rng, nhit si v nhit nng chy ca ankan

tng theo chiu tng ca s nguyn t cacbon c trong phn t.

Bng tnh cht vt l ca mt s ankan.

Nu biu din s ph thuc cu nhit nng chy ca cc hyrcacbon no mch thng

vo s nguyn t cacbon c trong phn t th ta s thu c th hnh rng ca.

Hp cht Cng thc phn t t0nc t0s dg/ml

Mtan

tan

Prpan

n-butan

n-pentan

n-hecxan

n-heptan

n-octan

n-nonan

n-kan

CH4 CH3CH3

CH3CH2CH3

CH3(CH2)2CH3

CH3(CH2)3CH3

CH3(CH2)4CH3

CH3(CH2)5CH3

CH3(CH2)6CH3

CH3(CH2)7CH3

CH3(CH2)8CH3

-183

-172

-187

-138

-135

-95

-90

-57

-54

-31

-162

-88,5

-42

0

36

69

89

126

151

174

0,625

0,659

0,684

0,703

0,718

0,730

47

Theo quy tc kinh nghim, tr mt s ankan thp nu mch ca phn t tng thm mt

nguyn t cacbon th nhit si ca ankan tng ln 20-300C.

Trn thc t 4 ankan u l nhng cht kh, 13 ankan tip theo (t C5 n C17) l cht

lng, t ankan C18 tr i l cht rn.

Ankan khng phn cc nn tan tt trong dung mi khng phn cc.

T trng ca cc ankan tng ln khi phn t lng tng nhng khng qu 0, 8 g/ml. iu

c ngha l ankan nh hn nc.

2.4. CC PHNG PHP IU CH.

Thng cc phng php iu ch cc hp cht hu c c chia lm 2 loi: phng

php cng nghip v phng php phng th nghim. Hai phng php ny c nhng im

khc nhau sau y:

Phng php cng nghip thng thu nhn mt khi lng hp cht ln vi gi thp

trong khi phng th nghim cn tng hp mt vi trm gam, mt vi gam hoc t hn, khng

quan tm n gi c v thi gian cn thit tng hp.

Phng php cng nghip s dng cc hp cht khng ch dng tinh khit m c dng

hn hp nhiu cht, cn trong phng th nghim lun lun i hi phi dng tinh khit.

Phng php cng nghip thng chn cch thu nhn hp cht sao cho thun li v vic

vn dng cc dy chuyn cng ngh v thit b. V vy thng phng php cng nghip ch c

ngha vi cch thu nhn mt hp cht nht nh. Tri li phng php phng th nghim quan

tm n vic s dng cho c mt lot hp cht cng loi vi nhau.

2.4.1. Phng php cng nghip.

a. Ngun thu nhn chnh ca ankan l du m v kh thin nhin. S thi ra hng triu

nm ca cc tng a cht chuyn ho cc hp cht hu c phc tp ca ng thc vt thnh

hn hp ankan c thnh phn t 1 n 30, 40 nguyn t cacbon. Thng kh thin nhin ch

cha nhng ankan nh (c phn t lng nh) ch yu l CH4. Du m c thnh phn ankan

phc tp hn. Bng phng php chng ct du m, ngi ta tch cc loi ankan ra khi nhau,

c ng dng rng ri trong i sng, cng nghip. Cc ankan l cht kh c s dng lm

-200

-150

-100

-50

0

50

1 3 5 7 9 11 13 15 17 19

S nguyn t C

Nhit

nng

ch

y

48nhin liu t. Cc ankan l cht lng c s dng lm nhin liu cho ng c dt trong, cc

ankan cao hn dng du (luille) dng bi trn. Cc ankan rn nh parafin dng lm nn

C Hn 2n+2cracking C Hm 2m+2 C H n-m 2(n-m)+

b. Phng php tng hp t xyt cacbon CO.

Cho hn hp xyt cacbon vi hyr nhit 2500C v p sut thng i qua xc tc

kim loi hay Co.

COn (2n-1)H2 C Hn 2n-2 nH2O+ +

2.4.2. Phng php phng th nghim.

a. Tng hp mtan t cacbua nhm. Al4C3 12H2O Al(OH)3 CH4+ +4 3

T sunfua cacbon CS2 CH4 Cu2S+ H2S2 + Cu8 + 4

T axtat natri (phng php kim nng chy) CH3COONa NaOH CH4 Na2CO3+ +

b. Tng hp tan: phn ng Vuyc.

CH3Cl CH3CH32 + Na2 NaCl2+ Phn ng Knbe: in phn mui axtat. Ti ant anion CH3COO- b phng in tch

thnh raical CH3COO. v b phn hu thnh CO2 v tan.

CH3COO. CH3CH3 CO22 +

c. Tng hp cc ankan cao hn.

Kh ho cc dn xut ankylhalogenua.

RX + Mg RMgXH2O RH ( RMgX l tc nhn Grinha)

CH3CH3CHBrCH3Mg CH3CH2CHMgBrCH3

H2O CH3CH2CH2CH3sec-butylbrmua n-butan

Kh bng kim loi trong mi trng axt.

CH3CH2CHBrCH3 Zn/H + CH3CH2CH2CH3

RX + Zn + H RH + Zn +2 + X

-+

Kh bng axt iic nhit cao.

RX + 2HICH3CH2CH2CH2CH2Cl + 2HI CH3CH2CH2CH2CH3 + HX + I2

RH + HX + I2

49d. Hyr ho anken.

C H C Hn 2n 2n+2nH2/Ni

Trong tt c cc phng php trn y, phng php hyr ho cc anken c ngha

nht v: phn ng tin hnh n gin (khuy trn mt anken vi hyr mt p sut va phi

v mt lng xc tc nh, ta s thu c mt ankan c khung cacbon ging nh anken ban

u). Mt khc ngun nguyn liu anken r, d thu nhn bng nhiu phng php khc nhau.

Kh ho cc ankylhalogenua bng tc nhn Grinha l phn ng th trc tip nguyn t

halogen bng hyr. Ankan thu c cng gi nguyn khung cacbon ban u. y cng l

phng php c ngha thc t ln v cc alkylhalogenua d dng thu nhn t cc hp cht

khc. Tuy nhin trong trng hp yu cu iu ch mt cht no m c th s dng c c

2 phng php th nn chn phng php hyr ho anken v n n gin hn v c hiu sut

phn ng cao hn. Phn ng Vuyc ch c ngha dng iu ch cc ankan i xng.

V d:

CH3CH2Br CH3CH2CH2CH3Na2CH3Br CH3CH3Na2

Trong trng hp dng iu ch cacbon bt i xng th phn ng Vuyc t c ngha

v to thnh mt hn hp sn phm do lm tng thm khi lng cht ban u v lm phc

tp qu trnh tch sn phm.

V d: + 2Na + + NaR1X R2X R1 R2

R2X2 R2 R22 R1X R1 R1 (sn phm ph)

(sn phm ph)

C ch ca phn ng Vuyc cho n nay vn cha c chng minh nhng trong c

hai giai on c bn l:

RX + 2Na RNa + NaXRNa + RX R-R + NaX

2.5. TNH CHT HO HC.

Ankan trc y gi l parafin (t ch latinh parumaffinis tc l i lc ho hc yu)

ni ln rng kh nng phn ng ca chng yu. Ankan khng c kh nng kt hp vi hyr nn

c gi l hyrcacbon no. Ankan khng phn ng trc tip vi clo, brm iu kin thng,

ch b oxy ho bi cc tc nhn oxy ha mnh nhit cao nh KMnO4.

Cc phn ng ca ankan.

1- Phn ng halogen ha.

50

R C H X2+ R C X HX+t 0 C

3- Phn ng vi iazmtan v kten.

R C H +

CH2N2iazmtan

CH2=C=Okten

as R C CH2 H + (N2 hay CO)

3- Phn ng t chy.

CO2O2+C H n 2n+2 3n+11 nH2O(n+1)+

4- Phn ng crcking.

C Hn 2n+2cracking C Hm 2m+2 C H n-m 2(n-m)+

5- Phn ng sunfnic ho:

R C H HO SO3H+ R C SO3H H2O+

6- Phn ng sunfclo ho:

R C H S O2 C l2 R C SO2Cl H Cl+ ++

7- Phn ng nitr ho:

+R C NO2 H 2O+R C H H O NO2

2.5.1. Phn ng halogen ho.

a. Trc ht ta nghin cu phn ng clo ho mtan.

Hn hp kh mtan v clo di tc dng ca nh sng hoc nhit (250-4000C) th

chng s tc dng mnh lit vi nhau to thnh phn t mtylclorua. Mtylclorua c th tip tc

tham gia phn ng clo ho to thnh mtylenclorua. Phn ng c th tip tc xy ra v to thnh

triclomtan (clorofoc) hoc ttraclomtan (cacbon ttraclorua).

CH4 CH3Cl CH2Cl2 CHCl3 CCl4Cl2 Cl2 Cl2 Cl2as as as as

V vy hiu r phn ng ta phi lm sng t my vn sau:

Mtan v clo khng tc dng vi nhau trong bng ti nhit thng. Phn ng d

dng xy ra trong bng ti nhit 2500C hoc nhit thng khi c chiu sng. Nu

phn ng c khi mo bng nh sng th c hng ngn phn t mtylclorua c to thnh

51khi phn ng hp th mt phton nh sng. Khi c mt lng nh oxy s lm gim tc phn

ng i mt thi gian. Thi gian ny ph thuc vo lng oxy c trong phn ng.

gii thch ph hp vi cc vn t ra trn y, ngi ta ngh mt c ch

tng qut cho phn ng clo ho mtan nh sau:

Cl2 t C0

Cl.

2CH4 Cl

.+ HClCH3

. +Cl

.CH3

.Cl2+ CH3Cl +

tip theo (2), (3), (2), (3)... Qu trnh vit phn ng ho hc theo tng giai on xy ra gi l c ch phn ng. Loi

c ch trn y gi l c ch gc. giai on (1) xy ra s ph v phn t clo thnh cc gc t

do cn mt nng lng ph v lin kt. Nng lng c cung cp bng s un nng hoc

chiu sng. Gc t do Cl. cng ging nh cc gc t do khc c kh nng phn ng rt mnh v

do n tm cch kt hp vi mt electron lm y lp 8 in t ca mnh. t c iu

gc Cl. cn phi va chm vi cc nguyn t hoc cc phn t khc. S va chm vi cc gc

t do Cl. khc c xc sut rt nh v rng nng ca chng to thnh mt thi im bt k

rt t. S va chm vi phn t clo ch dn n s thay i mt gc t do ny bng mt gc t do

khc m thi.

Cl. Cl.

Cl Cl Cl Cl+ +

V vy ch c s va chm vi phn t mtan mi dn n vic to thnh mt gc t do

mi (giai on 2).

Gc mtyl CH3. mi sinh ra cng tng t nh gc clo trc y tm cch lm y lp 8

in t ca mnh bng s va chm vi cc phn t hoc nguyn t khc. S va chm cng ch c

ngha vi phn t clo v mi to thnh mtylclorua v Cl. (giai on 3). Gc t do clo mi sinh

ra ny li tham gia vo phn ng (2), tip theo l phn ng (3). Qu trnh ny c lp i lp

li nhiu ln to thnh nhiu phn t mtylclorua.

Tuy nhin cc phn t trn y xy ra khng phi l vnh cu v rng tuy s va chm ca

cc gc t do vi nhau rt t nhng vn c th xy ra v do dn n s mt i cc gc t do:

Cl. Cl. Cl Cl+CH3

.+ CH3 CH3

.CH3Cl

.+CH3

.CH3 Cl

Nu trong phn ng c mt oxy th:

52

CH3.

O2+ CH3OO.

Gc t do CH3OO. C kh nng phn ng thp hn nhiu so vi gc CH3. nn lm cho

tc phn ng chm li. Hp cht c kh nng lm cho phn ng b chm li hoc lm dng

phn ng ngay c khi vi mt lng rt nh gi l cht c ch. Trong v d trn y oxy l cht

c ch CH3OO. l gc c ch.

iu cui cng chng ta cn phi gii thch l ti sao thu c mt hn hp nhiu sn

phm v c th khng ch phn ng thu c mt sn phm duy nht l mtylclorua hay

khng?

thi gian u ca phn ng, mtan tc dng vi clo to thnh mtylclorua (I). Theo

thi gian khi lng mtan bt dn v mtylclorua tng ln do mtylclorua s tham gia cnh

tranh vi mtan trong phn ng clo ho. Khi nng ca mtylclorua ln hn nng mtan th

clo s tc dng nhiu hn vi mtylclorua, II tr thnh ch yu. Tng t nh vy s xy ra cc

phn ng III, IV. V vy sn phm ca phn ng l mt hn hp 4 dn xut ankylhalogenua. C

th khng ch phn ng ch to ra mt sn phm ch yu l mtylclorua bng cch cho d

mtan. Trong trng hp ny lng mtan lun lun nhiu hn mtylclorua v do s hn ch

c phn ng II.

b. Phn ng dy chuyn.

Phn ng gia mtan v clo trn y ngi ta gi l phn ng dy chuyn tc l phn

ng xy ra qua nhiu giai on m trong giai on ny lm sinh ra nhng trung tm c kh

nng phn ng mnh gy ra phn ng ca giai on tip theo. y cng l phn ng c

trng cho cc hp cht ankan ni chung.

X. RH R.

+ + HXR. X2+ RX + X

.

R.+

X.X. + X2

X. R.+ RXR. R-R

tip theo (1), (2), (3)...

(2)(3)

Giai on pht trin mch

Giai on tt mch

(4)(5)(6)

X2250-400 C0

2X. (1)Giai on to gc

Trn gin nng lng ca phn ng clo ho mtan ta nhn thy rng E2, E3 c ngha

l trong hai phn ng pht trin mch, phn ng (2) xy ra chm hn nhiu so vi (3) do

phn ng (2) c tnh cht quyt nh tc phn ng.

53

E3

E2

CH4+Cl.

CH3. + Cl2 CH3Cl+ Cl.

E

tin trnh phn ng

trng thi chuyn tip

c. nh hng phn ng halogen ho.

Xt cc phn ng halogen ho cc hp cht sau:

CH4 Cl.

CH3. Cl2 CH3Cl

Cl.CH3CH3 CH3CH2. Cl2 CH3CH2Cl

CH3 CH CH2H

H

CH3CH2CH2. CH3CH2CH2Cl

CH3CHClCH3

gc n-prpyl n-prpylclorua

gc izpropyl izpropylcloruaCH3CHCH3

.

Cl.

Cl. Cl2

Cl2

Trong phn ng ca prpan vi clo, gc prpyl c to thnh khi tch i mt hyr bc

I, izprpyl c to thnh khi tch hyr bc II. Ta nhn thy rng trong phn t prpan c 6

hyr bc I v 2 hyr bc II nn xc sut va chm ca Cl. vi cc loi hyr ny l 6:2 (hay

3:1) c ngha l sn phm n-prpylclorua: izprpylclorua l 3:1. Nhng trong thc t t l thu

c l 1:1 (45:55). Ngha l izprpylclorua c to thnh vo khong 3 ln nhiu hn l

n-prpylclorua. iu ch c th gii thch bng nng lng hot ho Ea (Ea dng tch

hyr bc II nh hn rt nhiu so vi hyr bc I). Bng s kho st tng t ngi ta i n

kt lun rng kh nng tham gia phn ng halogen ho ca cc nguyn t hyr bin i theo

dy sau:

Hyr bc I < Hyr bc II < Hyr bc III

nhit phng t l vo khong 5,0:3,8:1,0. T l ny cho php tin on t l cc

sn phm sinh ra trong mt phn ng clo ho.

V du:

CH3CH2CH2CH3Cl2/as CH3CH2CH2CH2Cl CH3CH2CHClCH3

n-butylclorua izbutylclorua

+

Ta c t l sn phm:

54n-butylcloruaizbutylclorua=

s hyr bc Is hyr bc II

kh nng phn ng hyro bc Ikh nng phn ng hyro bc II

= 64

1,03,8

= = 28%72%

615,2

Kh nng tham gia phn ng ca hyr vi brm xy ra theo t l hyr bc I : hyr

bc II : hyr bc III = 1600 : 82 : 1

S d kh nng tham gia phn ng ca cc loi hyr trong phn ng halogen ho

thay i nh trn l v do nh hng ca hiu ng +I ca cc nhm ankyl nn dn n bn

ca cc raical bin i nh sau:

CH3 C

CH3

CH3

. CH3 C

CH3

H

. CH3 C

H

H

. H C

H

H

.

c. S xut hin nguyn t cacbon bt i xng.

Trong phn ng clo ho n-butan c sn phm thu c sec-butylclorua c nguyn t C2

bt i, nhng thc nghim chng minh rng sec-butylclorua l mt hp cht khng quang hot.

iu c gii thch rng giai on (2) gc Cl. tch i mt nguyn t hyr bc II to thnh

sec-butylclorua. Nguyn t cacbon trong gc t do c ocbitan lai to sp2. Giai on tip theo

to thnh lin kt C-Cl clo c th tn cng c t hai pha ca mt phng cha ocbitan lai to sp2.

V xc sut tn cng vo hai pha ca mt phng nh nhau nn to thnh mt s lng bng

nhau cc sn phm quay phi v quay tri, do gc quay ca nh sng phn cc trit tiu ln

nhau nn hn hp sn phm thu c khng quang hot. Ngi ta gi hn hp ny l bin th

Raxmic.

H3C

C2H5

HCl2

a

b

CH3

C2H5

HCl

HCl

H3C

C2H5

CH3

C2H5

ClHCl H

CH3

C2H5

Vy hn hp Raxmic tc l hn hp mt s lng bng nhau ca ng phn quang hc

quay phi v quay tri. Phn ng to thnh hn hp Raxmic gi l phn ng Raxmic ho.

2.5.2. Mtylen ho.

Mtylen c to thnh trong phn ng phn tch cc hp cht iazmtan hoc xten

di tc dng ca nhit:

55

t C0CH2 C O CH2 CO+

t C0CH2 N+ N- CH2 N2+

Mtylen c tnh hot ng ho hc mnh v do tham gia phn ng mtylen ho:

CH3CH2CH2CH2CH2CH3

CH3CH2CH2CH(CH3)2

CH3CH2CHCH2CH3CH3

CH3CH2CH2CH2CH3CH2N2

t C0

n-hecxan

2-mtylpentan

3-mtylpentan

CH3CH2CH2CH3CH2 C O

t C0CH3CH2CH2CH2CH3 CH3CH2CHCH3

CH3

+

2.5.3. Phn ng t chy.

Phn ng ankan vi xy to thnh CO2 v nc cng vi s gii phng mt nng lng

ln thng c s dng thu nng lng. Cho n nay c ch ca phn ng ny cha c

chng minh nhng chc chn rng y l phn ng dy chuyn c ch gc. Mt trong nhng

ng dng rt quan trng ca phn ng ny l dng nhit t chy cc hyrcacbon chy cc

ng c t trong. Vic s dng cc ng c p sut cao c ngha rt ln nhng lm xut

hin mt kh khn: nhin liu trong xylanh thng t n nhng thi im cha cn thit nn

lm gim sc my. khc phc iu ny ngi ta khc phc bng hai phng php:

1- Chn nhng hyrcacbon thch hp lm nhin liu ng c.

2- Cho thm hp cht ttramtyl ch vo nhin liu.

Theo phng php th nht ngi ta phn loi rng hyrcacbon tt nht lm

nhin liu ng c l hp cht izoctan.

CH3C(CH3)2CH2CH(CH3)2

2,2,4-trimtylpentan (izoctan)

Ngi ta quy nh izoctan c ch s octan l 100. Hp cht c ch s octan km nht l

n-heptan (bng 0). Ch s octan ca nhin liu tng ln rt mnh khi cho thm mt lng

ttratyl ch.

56CU HI N TP V BI TP CHNG 2

2.1. Gi tn ankan theo danh php thng thng v danh php IUPAC.

2.2. Cc phng php iu ch ankan.

2.3. Nhng tnh cht ha hc quan trng ca ankan.

2.4. Vit phng trnh phn ng iu ch cc ankan sau y:

a. n-Butan

b. iz-pentan

2.5. Khi Clo ha cc ankan sau y trong iu kin c nh sng xc tc s thu c nhng dn

xut mono Clo g?

a. n-Propan

b. Iz-butan

Tnh hiu sut cc sn phm trong mi trng hp, gi s kh nng phn ng ca cc

nguyn t hiro cacbon bc I, bc II, bc III tng ng vi: 1:3:5

2.6. Gi tn theo danh php quc t cc hp cht sau y: CH3 CH2 CH

C2H5

CH

CH3

CH2 CH3 CH3 CH2 CH

CH3

CH

C2H5

CH3

CH3 C

CH3

CH3

CH2 CH

CH CH3CH2CH3

CH2 CH

CH3

CH2 CH3 CH3 CH2 C

C2H5CH2 CH3

C2H5

a. b.

c. d.

2.7. Cho bit cc sn phm ph trong phn ng iu ch n-pentan t n-propyl ioua v etyl

ioua theo phng php tng hp WURTZ (Vuyc).

TI LIU THAM KHO CA BI TP CHNG 2

[1]. Chu Phm Ngc Sn, Nguyn Hu Tnh, Nguyn Huy Ngc, L Khc Tch, Bi tp

ha hc hu c.

[2]. Ng th Thun, Bi tp ha hc hu c (2008), Nxb. Khoa hc v K thut, H Ni.

[3]. Thi Don Tnh, Bi tp c s l thuyt ha hu c (2005), Nxb. Khoa hc v K thut,

H Ni.

[4]. Thi Don Tnh, Bi tp c s ha hc hu c (2005), Nxb. Khoa hc v K thut, H

Ni.

[5]. Nguyn th Bch Tuyt (1995), Gio trnh ha hu c, Hu.

57Chng 3

ANKEN

Anken l loi hyrcacbon c s lng nguyn t hyr trong phn t t hn trong

ankan tng ng l hai nguyn t. V n c kh nng cng hp vi hyr nn c gi l

hyrcacbon cha no. Cng thc tng qut ca anken l CnH2n.

3.1. CU TO V NG PHN CA ANKEN.

3.1.1. Cu to.

Cu to n gin nht ca dy anken l tylen C2H4, trong phn t tylen 2 nguyn t

cacbon u c ocbitan lai to l sp2. Cc ocbitan lai to ny xen ph vi ocbitan s ca hyr vo

vi nhau to thnh 5 lin kt nm trong mt mt phng. Mi nguyn t cacbon cn li mt in t t do xen ph vi nhau to thnh lin kt (2 m my in t nm pha trn v pha di ca mt phng cha lin kt ).

C CH

H

H

H

H

H

H

H

C 1,34A C0

1,09A0

117,50

1210 Hp cht tip theo l prpen C3H6 c cu to l CH3-CH=CH2.

Tip theo l butylen c mt s cu to:

CH3CH2 CH CH2 CH3 CH CH CH3 CH3 C CH2CH3

buten-1 buten-2 izbuten Hp cht buten-2 c th vit di 2 dng ng phn hnh hc:

C CHH

CH3H3CC C

H

H CH3

H3Ccis-buten-2 trans-buten-2

3.1.2. ng phn hnh hc.

ng phn hnh hc l loi ng phn xut hin do s cn tr quay t do ca cc nguyn

t xung quanh lin kt i C=C. Ngi ta k hiu cc ng phn c hai nhm th hoc hai

nguyn t ging nhau nm v cng mt pha cu mt phng l ng phn cis, nu nm khc pha l ng phn trans.

Tt nhin s cn tr quay xung quanh lin kt i i vi cc nguyn t cacbon ca

anken no cng c th nhng ng phn hnh hc ch xut hin khi no cc nhm th cc

nguyn t cacbon ni i khc nhau.

58V d:

C CHH

H3C HC C

H

H H

C2H5

CH3C C

H

H CH3

Khng c ng phn hnh hc

C CH H

ClClC C

H

H

Cl

Clcis-icloten trans-icloten

c im ca cc ng phn hnh hc l chng c cc tnh cht vt l khc nhau, c cc

tnh cht ho hc tng t nhau v cng mt loi hp cht nhng mc tham gia cc phn ng

ho hc ca chng khc nhau v c cu to hnh hc khc nhau.