Question

2-methylpropane is chlorinated. The major product is

• A. 1-chloro-2-methylpropane
• B. 2-chloro-2-methylpropane
• C. Both are equally formed
• D. 2-chloro-2-methylpropane is obtained in excess, slightly.

Answer 1

The correct option is A 1-chloro-2-methylpropane

The relative rates of displacements of $1^o$ and $3^o$ H atoms present in 2-methylpropane by chlorine are 1:5.
Total relative rates of displacement of nine $1^o$ H, whose displacement gives 1-chloro-2-methylpropane is, 9 x 1 =9.
Relative rate of displacement of one $3^o$ H, whose displacement gives 2-chloro-2-methylpropane is 1 x 5 = 5.
% 1-chloro-2-methylpropane
$=\frac{9\times 100}{14}=64\%$ (apprx.)
% yield of 2-chloro-2-methylpropane
$=\frac{5}{14}\times 100=35.6\%$ (apprx.)
So, major product is 1-chloro-2-methylpropane.