CambridgeInternationalASandALevelChemistry OriginalmaterialCambridgeUniversityPress2011 1

Worksheet14.2

Alkeneselectrophilicaddition

1 Etheneandbrominereacttogethertogive1,2dibromoethane.a Writeabalancedsymbolequationforthisreaction. [1]b Explainthemechanismforthisreactionusingcurlyarrows.Youshouldinclude:

the instantaneousdipoleonthebrominemoleculeatthestart theattackonthebrominemoleculebyanelectronpair(curlyarrow)fromthebond thebreakingofthebrominebrominebond(curlyarrow) thepositiveionformedasanintermediate thebondforming(curlyarrow)fromthebromideiontothispositiveion. [5]

2 Etheneandhydrogenbromidereacttogethertogivebromoethane.a Writeabalancedsymbolequationforthisreaction. [1]b Explainthemechanismforthisreactionusingcurlyarrows.Youshouldinclude:

thedipoleonthehydrogenbromidemoleculeatthestart theattackonthehydrogenbromidemoleculebyanelectronpair(curlyarrow)from

thebond thebreakingofthehydrogenbrominebond(curlyarrow) thepositiveionformedasanintermediate thebondforming(curlyarrow)fromthebromideiontothispositiveion. [5]

3 Propeneandsteamreacttogethertogivetwoisomericproducts.a Writeabalancedsymbolequationforthisreaction. [1]b Namethecatalystthatisusedtospeedupthisreaction. [1]c Givenamesandfullstructuralformulaeofthetwo isomericproducts. [4]d Explainthemechanismforthisreactionusingcurlyarrows.Youshouldinclude:

thedipoleonthewatermoleculeatthestart theattackonthewatermoleculebyanelectronpair(curlyarrow)fromthebond thebreakingofthehydrogenoxygenbond(curlyarrow) thepositiveionformedasanintermediate thebondforming(curlyarrow)fromthehydroxideiontothispositiveion. [5]

4 Useoneofthereactionsaboveasasourceofexamplestoexplainwhatismeantbythefollowingterms.a electrophile [2]b addition [2]c heterolyticfission [2]