Answer to Question #86377 in Organic Chemistry for Gayatri

Question

3-Bromocyclohex-1-ene or 2-Bromocyclohex-1-ene, which would undergo a faster SN1 reaction?

Answer 1

Since the first step of the SN1 reaction is loss of a leaving group to give a carbocation, the rate of the reaction will be proportional to the stability of the carbocation. Carbocation stability increases with increasing substitution of the carbon (tertiary > secondary >> primary) as well as with resonance.

The carbocation formed from 3-bromocyclohex-1-ene is more stable than carbocation formed from 2-bromocyclohex-1-ene as the first one has two resonance structures. Consequently 3-Bromocyclohex-1-ene would undergo a faster SN1 reaction.