Question

The correct order of reactivity of the following types of H atom towards radical substitution is:

• A. $allylic>vinylic>1^{o}H$
• B. $allylic>1^{o}H>vinylic$
• C. $1^{o}H>allylic>vinylic$
• D. $vinylic>allylic>1^{o}C$

Answer 1

The correct option is B $allylic>1^{o}H>vinylic$

Radical substitutions are those reactions in which a free radical intermediate is produced. So, the rate of the radical substitution reaction is directly proportional to the stability of the free radical formed.

Now we know that the order of stability is $s{p}^3>s{p}^2>sp$. Also, due to +I effect of primary radical, allylic radical is more stable than primary, secondary and tertiary radicals.

Vinylic radical will be the least stable because of $s{p}^2$ hybridization

Therefore, the correct answer will be option B