Question

The correct decreasing order of dehydration of following alcohols with concentrated $H_{2}S{O}_4$ is:

• A. C > D > A > b
• B. D > A > C > B
• C. A > B > C > D
• D. D > C > A > B

Answer 1

The correct option is A C > D > A > b

Dehydration of alcohol in the presence of an acid involves the loss of -OH and formation of carbocation. Reactivity is directly proportional to the stability of the carbocation.

In C, the carbocation is tertiary and most stable. It is further stabilised by the conjugation with double bond.

Next will be A which gives a secondary carbocation stabilised by conjugation by double bond.

B also gives a secondary carbocation, but here double bond is not in conjugation.

In D the formation of a secondary carbocation results in a conjugated cyclic structure with 4$\pi$ electrons.

So the reactive order will be C > D > A > B