JEE MAIN - Chemistry (2006 - No. 9)
The increasing order of stability of the following free radicals is
$${({C_6}{H_5})_2}\mathop C\limits^ \bullet H$$ < $${({C_6}{H_5})_3}\mathop C\limits^ \bullet$$ < $${(C{H_3})_3}\mathop C\limits^ \bullet $$ < $${(C{H_3})_2}\mathop C\limits^ \bullet H$$
$${(C{H_3})_2}\mathop C\limits^ \bullet H$$ < $${(C{H_3})_3}\mathop C\limits^ \bullet $$ < $${({C_6}{H_5})_2}\mathop C\limits^ \bullet H$$ < $${({C_6}{H_5})_3}\mathop C\limits^ \bullet$$
$${(C{H_3})_2}\mathop C\limits^ \bullet H$$ < $${(C{H_3})_3}\mathop C\limits^ \bullet $$ < $${({C_6}{H_5})_3}\mathop C\limits^ \bullet$$ < $${({C_6}{H_5})_2}\mathop C\limits^ \bullet H$$
$${({C_6}{H_5})_3}\mathop C\limits^ \bullet$$ < $${({C_6}{H_5})_2}\mathop C\limits^ \bullet H$$ < $${(C{H_3})_3}\mathop C\limits^ \bullet $$ < $${(C{H_3})_2}\mathop C\limits^ \bullet H$$
Explication
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.
$${\left( {{C_6}{H_5}} \right)_3}\,\mathop C\limits^ \bullet > {\left( {{C_6}{H_5}} \right)_2}\mathop C\limits^ \bullet H > {\left( {C{H_3}} \right)_3}\mathop C\limits^ \bullet > {\left( {C{H_3}} \right)_2}\mathop C\limits^ \bullet H$$
The stabilisation of first two is due to resonance and last two is due to inductive effect.