Question

Halogenation is a substitution reaction, where halogen replaces one or more hydrogens of hydrocarbon.
Chlorine free radical make $1^{\circ },2^{\circ },3^{\circ }$ radicals with almost equal ease, whereas bromine free radicals have a clear preference for the formation of tertiary free radicals. So , bromine is less reactive, and more selective whereas chlorine is less selective and more effective.
The relative rate of abstraction of hydrogen by Br is
$\underset{\left(1600\right)}{3^{\circ }}>\underset{\left(82\right)}{2^{\circ }}>\underset{\left(1\right)}{1^{\circ }}$
The relative rate of abstraction of hydrogen by Cl is
$\underset{\left(5\right)}{3^{\circ }}>\underset{\left(3.8\right)}{2^{\circ }}>\underset{\left(1\right)}{1^{\circ }}$
B.Above product will obtained in better yield if X is

• A. $C{l}_2$
• B. $I_2$
• C. $B{r}_2$
• D. Can't be predicted

Answer 1

Answer: (C)

$B{r}_2$

For the reaction $R-H+X_2\stackrel{h\nu }{⟶}R-X+HX$ to be obtained in better yeild, $X$ must be Bromine, This is because $R$ is a $3^o$ radical, hence we know relative rate of Bromination is very high.