electrophilic addition

what is an electrophile?

e^- deficient species which will accept a pair of e^-

what is a carbocation?

+vely charged C atom w/ only 3 bonds, making it unstable

what does electrophilic addition involve? what does it form?

alkene → dihaloalkane

draw out the electrophilic addition mechanism between HBr and propene (for both the major and minor product):

draw out the electrophilic addition mechanism between Br₂ and ethene:

draw out the electrophilic addition mechanism between H₂SO₄ and ethene and state the conditions:

give the order of carbocation stability - why is this the case?

• tertiary carbocations have the most stability as they have the greatest +ve inductive effect as they have the most alkyl/C groups

• as they push e^- density towards the carbocation and stabilise the +ve charge

• the more alkyl groups, the more stable

what is a primary carbocation?

carbocation w/ only 1 alkyl group

what is a secondary carbocation?

carbocation w/ 2 alkyl groups

what is a tertiary carbocation?

carbocation w/ 3 alkyl groups

why may a product of electrophilic addition display optical isomerism?

• electrophilic addition involving an alkene w/ one of the Hs substituted for a different functional group e.g. CN + HX

• product is a haloalkane w/ one of the Hs subbed for the other functional group

• one of the carbocations may form a product w/ a chiral C

• optical as C+ on carbocation planar so can be attacked from above or below

there is a very low yield of butan-1-ol from but-1-ene in this manufacturing process - explain why (2)

• formed from less stable carbocation

• formed from 1^o rather than 2^o carbocation