Question

The decreasing order of reactivity towards dehydrohalogenation $\left(E1\right)$ reaction of the following compounds is :
(A)
(B)
(C)
(d)

• A. $D>B>C>A$
• B. $B>D>C>A$
• C. $B>A>D>C$
• D. $B>D>A>C$

Answer 1

The correct option is A $D>B>C>A$

Rate of $E1$ reaction depends only the substrate.
$\text{Rate of dehydrohalogen (}E1)\propto \text{stability of carbocation formed}$

Compound (d) and (b) forms stable allylic cation but (d) is also stabilised by +I effect of methyl group. Hence, it is more stable.

Among (a) and (c), secondary carbocation formed by (c) is more stable than primary carbocation of (a)

Hence, order of stability of carbocation formed is,
$D>B>C>A$

Hence, order of reactivity is,
$D>B>C>A$