Chemistry - GOC Question with Solution | TestHub
For each transformation below, complete the mechanism by drawing the proper arrows. The number of reactions that proceed through a carbocation intermediate is :
(a) 
(b) 
(c) 
(d) 
Options:
Answer:
Solution:
(a) SN2: The hydroxide attacks the carbon from the side opposite the C-Br bond, while the C-Br electron pair leaves with Br-. This is a one-step reaction with no intermediate.
(b) SN1: The C-Cl bond breaks first, yielding a planar tertiary carbocation and Cl-. Bromide then attacks the carbocation. This reaction proceeds via a carbocation intermediate.
(c) E2: The alkoxide base removes a β-hydrogen. Simultaneously, the C-H electrons form a π bond, and the C-Br electron pair leaves with Br-. This is a one-step reaction with no intermediate.
(d) E1: The C-Br bond breaks first, forming a tertiary carbocation. Subsequent loss of a β-hydrogen then forms the alkene. Both (b) and (d) proceed through a carbocation intermediate. Therefore, there are 2 reactions that go through a carbocation, making the answer (D).
