Question

Isobutane is subjected to bromination. The major product is

• A. Isobutyl bromide
• B. Tert-butyl bromide
• C. Both are equally formed
• D. Isobutyl bromide slightly in excess

Answer 1

The correct option is B Tert-butyl bromide

Relative rates of $1^o$ and $3^{o}H$ atoms by bromine are 1:1600.
Tert butyl bromide is formed by displacement of $3^o$ H. It is only one in number. Its relative rate of displacement by bromine is 1600.
Formation of 1-bromo-2-methyl propane (Isobutyl bromide) takes place by replacemnt of any of the nine $1^o$ H atoms. But relative rate of displacement of $1^o$ H is 1. Total relative rate of displacement of all the nine $1^o$ H atoms is 9.
% of tert butyl bromide = $\frac{1600}{1609}\times 100=>90\%$
% of iso butyl bromide = $\frac{9}{1609}\times 100=<10\%$
So, major product is tert-butyl bromide.