Question

The rate of the reaction

is influenced by the hyperconjugation effect of group $R$. If $R$ sequentially is
the increasing order of speed of the above reaction is

• A. IV, III, II, I
• B. I, II, III, IV
• C. I, IV, III, II
• D. III, II, I, IV

Answer 1

Answer: (A)

More the number of $H$-atoms on the $\alpha$-carbon of the group $R$, more are the hyperconjugating structures, weaker is the $C-Br$ bond and hence, ethyl has two, iso-propyl has one and tert-butyl group has no $\alpha$-hydrogen therefore, hyperconjugation effect decreases and hence the rate decreases in the same order.