Question

The rate of the reaction

is influenced by the hyperconjugation effect of group $R$. If $R$ sequentially is
I. $\quad CH _{3}-$
II. $CH _{3}- CH _{2}-$
III. $H_3C -\underset{CH}{\underset{|}{CH_3}}$
Iv.
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, higher is the rate of the reaction. Now since $CH _{3}$ has three, 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.