Above product will be obtained in better yield if X is : | TestHub

Passage / Comprehension

Halogenation is a substitution reaction, where halogen replaces one or more hydrogens of hydrocarbon.

$R - H + X_{2} h ν R - X + H X$

Chlorine free radicals form 1°, 2°, and 3° radicals with almost equal ease, whereas bromine free radicals show a clear preference for the formation of tertiary free radicals. Therefore, bromine is less reactive and more selective, while chlorine is more reactive and less selective.

The relative rate of abstraction of hydrogen by Br• is:

3° > 2° > 1°

(1600) (82) (1)

The relative rate of abstraction of hydrogen by Cl• is:

3° > 2° > 1°

(5) (3.8) (1)

Above product will be obtained in better yield if X is :

Options:

Answer:

Solution:

Question Explanation: Select the halogen that shows maximum selectivity during substitution so as to obtain a higher yield of a specific isomer.

Concept:

This question is based on the relative reactivity and selectivity of halogens in free-radical halogenation reactions.

Solution:

If X is Br then % of A = $\frac{1600 \times 1}{1600 \times 1 + 3 \times 1 + 10 \times 82} \times 100$

$\frac{1600}{1600 + 3 + 820} \times 100 = 66.03%$

If X is Cl then % of A = $\frac{5 \times 1}{5 \times 1 + 3 \times 1 + 10 \times 3.8} \times 100$

$\frac{5}{5 + 3 + 38} \times 100 = \frac{5}{46} \times 100 = 10.87%$

Chemistry - Hydrocarbon Question with Solution | TestHub

Options:

Doubts & Discussion