Question

A secondary butyl free radical is more stable than the primary butyl free radical. It is due to the

• A. $-I$ effect of the $-C{H}_3$ group
• B. $+R$ effect of the $-C{H}_3$ group
• C. $-R$ effect of the $-C{H}_3$ group
• D. Hyperconjugation

Answer 1

The correct option is D Hyperconjugation

$\underset{\text{sec-butyl radical (5}\alpha \text{-H)}}{C{H}_3-C{H}_2-\stackrel{\cdot }{C}H-C{H}_3}<\underset{\text{primary butyl radical (2}\alpha \text{-H)}}{C{H}_3-C{H}_2-C{H}_2-\stackrel{\cdot }{C}{H}_2}$

More the number of $\alpha$-H, more will be the stability of the free radical. Therefore, due to the higher number of $\alpha$-H, the sec-butyl radical is more stable than the primary butyl radical.

Hence, option (d) is the correct answer.