Question

The increasing order of stability of the following free radicals is :
A. `(CH_(3))_(2)overset(*)(C)H lt (CH_(3))_(3) overset(*)(C) lt (C_(6)H_(5))_(2) overset(*)(C)H lt (C_(6)H_(5))_(3)overset(*)(C)`
B. `(C_(6)H_(5))_(3)overset(*)(C) lt (C_(6)H_(5))_(2)overset(*)(C)H lt (CH_(3))_(3) overset(*)(C) lt (CH_(3))_(2)overset(*)(C)H`
C. `(C_(6)H_(5))_(2)overset(*)(C)H lt (C_(6)H_(5))_(3)overset(*)(C) lt (CH_(3))_(3)overset(*)(C) lt (CH_(3))_(2)overset(*)(C)H`
D. `(CH_(3))_(2)overset(*)(C)H lt (CH_(3))_(3)overset(*)(C) lt (C_(6)H_(5))_(3) overset(*)(C) lt (C_(6)H_(5))_(2) overset(*)(C)H`

Answer 1

Correct Answer - A
`(C_(6)H_(5))_(3)overset(*)(C)` and `(C_(6)H_(5))_(3)overset(*)` is more resonance stabilised. `(CH_(3))_(2)overset(*)(C)H` (6 hyperconjugative structures) and `(CH_(3))_(3)overset(*)(C)` (9 hyperconjugative structures) are stabilized through hyperconjugation. Larger the number of hyperconjugative structure, greater the stability. Resonanace proves a better way to provide stability rather than hyperconjugation.
Therefore stability order goes as
`(CH_(3))_(2)overset(*)(C)H lt (CH_(3))_(3) overset(*)(C)lt (C_(6)H_(5))_(2)overset(*)(C)H lt (C_(6)H_(5))_(3)overset(*)(C)`