Arac&ve)Forces:)Boiling)and) …...... 36.1) C • Hexane)))))68.7) C • Heptane)))))98.4) C •...
Transcript of Arac&ve)Forces:)Boiling)and) …...... 36.1) C • Hexane)))))68.7) C • Heptane)))))98.4) C •...
A"rac&ve Forces: Boiling and Mel&ng Points and Bicyclic System
Boiling Points
The greater the a"rac&ve forces between molecules, the higher the boiling point.
A"rac&ve forces
Boiling Points
• Methane 167.7 °C • Ethane –88.6 °C • Propane –42.1 °C • Butane –0.5 °C • Pentane 36.1 °C • Hexane 68.7 °C • Heptane 98.4 °C • Octane 125.7 °C
induced dipole-‐induced dipole interac&ons
van der Waals forces
The greater the surface area of the molecule,
the higher the boiling point.
Branching Lowers the Boiling Point
“cigar” “tennis ball”
Dipole–Dipole Interac&ons
Van der Waals Van der Waals dipole–dipole
Dipole–dipole interac&ons are stronger than van der Waals forces.
Compara&ve Boiling Points
Compara&ve Boiling Points
The larger the halogen, the more polarizable it is.
Hydrogen Bonds in H2O and NH3
CH4 –167.7 °C H2O 100 °C no hydrogen bonds hydrogen bonds
Hydrogen bonds are stronger than other dipole–dipole interac&ons.
Hydrogen Bonds in Water
Hydrogen Bonds in Amines
Hydrogen bonds are stronger in primary amines than in secondary amines because primary amines have stronger dipole–dipole interac&ons.
Ter&ary amines cannot form hydrogen bonds with each other.
Hydrogen Bonds in Proteins
Compounds with Similar Shapes and Proper&es O]en Have Similar Physiological Ac&vi&es
Drugs bind to their receptors by van der Waals interac&ons, dipole-‐dipole interac&ons, and hydrogen bonding.
Mel&ng Points
alkanes with an odd number of carbons pack less &ghtly. The mp is influenced by the packing of the molecules in the crystal la`ce
Solubility
like dissolves like
Polar compounds dissolve in polar solvents (H2O).
Nonpolar compounds dissolve in nonpolar solvents (hexane).
Solva&on
Solva&on is the interac&on between solute molecules and solvent molecules.
An Oxygen Can Drag Three Carbons Into Water
“Like Dissolves Like” is Important in Drug Ac&on
Crossing the blood–brain barrier requires a fat-‐soluble drug.
THC and barbiturates have a hydrocarbon tail to facilitate crossing the barrier.
Solubili&es of Alkyl Halides
• Boiling points and mel&ng points increase as size of alkane increases • Dispersion forces increase as molecule size increases, resul&ng in higher
mel&ng and boiling points
Physical Proper&es of Alkanes
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Decalin
Cis-‐decalin has a ring fusion where the second ring is a"ached by two cis bonds. Trans-‐decalin is fused using two trans bonds. Trans-‐decalin is more stable because the alkyl groups are equatorial.
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Bicyclic Systems
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Nomenclature of Bicyclic Systems
Bicyclo [#.#.#]alkane
Where # are the number of carbons on the bridges (in decreasing order) and the alkane name includes all the
carbons in the compound.