Question

The ease of formation of free radicals follows the order:
A.\[3^\circ > 2^\circ > 1^\circ > {\text{C}}{{\text{H}}_{\text{3}}}\]
B.\[{\text{C}}{{\text{H}}_{\text{3}}} > 1^\circ > 2^\circ > 3^\circ \]
C.\[1^\circ > 2^\circ > 3^\circ > {\text{C}}{{\text{H}}_{\text{3}}}\]
D.\[2^\circ > 1^\circ > 3^\circ > {\text{C}}{{\text{H}}_{\text{3}}}\]

Answer 1

Hint: The more stable a free radical is the more will be its tendency to form or more easily it forms. The stability of free radicals can be determined by the inductive effect, more is the inductive effect, more is the stability of free radicals.

Complete step by step answer:
Radicals are the species which contains at least one unpaired electron. The basic free radical containing carbon is methyl free-radical that is \[ \bullet {\text{C}}{{\text{H}}_{\text{3}}}\]. Free radicals can be classified into three categories primary free radical, secondary free radical and tertiary free radical.
Primary free radical \[1^\circ \] is that in which carbon containing unpaired electron is connected to only one alkyl group and secondary free radical, \[2^\circ \] is that in which it is connected to only two carbons and tertiary, \[3^\circ \] is that in which it is connected to three alkyl groups.
Since carbon has four valence, if 3 hydrogen atoms are attached to it than one valancy remain unbalanced which makes a free radical. Alkyl group have electron donating tendency or positive inductive effect that is when they are attached to carbon chain they give electron to the carbon. Since free radicals are already electron deficient species due to incomplete octet and if electron density is increased by inductive effect, it will increase the stability of the free radical. More are the number of alkyl groups; more will be the inductive effect and hence more will be stability. So tertiary free radical is most stable and hence easily forms and alkyl free radical due to no inductive effect forms very slowly because it is least stable.
The correct order is \[3^\circ > 2^\circ > 1^\circ > {\text{C}}{{\text{H}}_{\text{3}}}\].

Hence, the correct option is A.

Note:
Inductive effect is termed as the partial shift of sigma electrons through the carbon chain due to the presence of a certain group. The bigger the carbon chain more will be its inductive effect. Branched chains have more positive inductive effect than straight chains.