Question
The increasing order of stability of the following free radicals
is
A.
$${\left( {{C_6}{H_5}} \right)_2}\mathop C\limits^ \bullet H < {\left( {{C_6}{H_5}} \right)_3}\mathop C\limits^ \bullet < {\left( {C{H_3}} \right)_3}\mathop C\limits^ \bullet < {\left( {C{H_3}} \right)_2}\mathop C\limits^ \bullet H$$
B.
$${\left( {C{H_3}} \right)_2}\mathop C\limits^ \bullet H < {\left( {C{H_3}} \right)_3}\mathop C\limits^ \bullet < {\left( {{C_6}{H_5}} \right)_2}\mathop C\limits^ \bullet H < {\left( {{C_6}{H_5}} \right)_3}\mathop C\limits^ \bullet $$
C.
$${\left( {C{H_3}} \right)_2}\mathop C\limits^ \bullet H < {\left( {C{H_3}} \right)_3}\mathop C\limits^ \bullet < {\left( {{C_6}{H_5}} \right)_2}\mathop C\limits^ \bullet H < {\left( {{C_6}{H_5}} \right)_3}\mathop C\limits^ \bullet $$
D.
$${\left( {{C_6}{H_5}} \right)_3}\mathop C\limits^ \bullet < {\left( {{C_6}{H_5}} \right)_2}\mathop C\limits^ \bullet H < {\left( {C{H_3}} \right)_3}\mathop C\limits^ \bullet < {\left( {C{H_3}} \right)_2}\mathop C\limits^ \bullet H$$
Answer :
$${\left( {C{H_3}} \right)_2}\mathop C\limits^ \bullet H < {\left( {C{H_3}} \right)_3}\mathop C\limits^ \bullet < {\left( {{C_6}{H_5}} \right)_2}\mathop C\limits^ \bullet H < {\left( {{C_6}{H_5}} \right)_3}\mathop C\limits^ \bullet $$
Solution :
The order of stability of free radicals
$${\left( {{C_6}{H_5}} \right)_3}\mathop C\limits^ \bullet > {\left( {{C_6}{H_5}} \right)_2}\mathop C\limits^ \bullet H > {\left( {C{H_3}} \right)_3}\mathop C\limits^ \bullet > {\left( {C{H_3}} \right)_2}\mathop C\limits^ \bullet H$$
The stabilisation of first two is due to resonance and last two is due to inductive effect.