Question

Which of the following orders regarding relative stability of free radicals is correct?

• A.
  $$3^o<2^o<1^o$$
• B.
  $$3^o>2^o>1^o$$
• C.
  $$1^o<2^o>3^o$$
• D. $$3^o>2^o<1^o$$

Answer 1

The correct option is B

$$3^o>2^o>1^o$$
Due to increasing number of hyperconjugative structures free radicals stabilize following as $3^o>2^o>1^o$
The stabilisation of first two is due to hyperconjugation.
$3^o$ free radical will have more resonance due to more R(alkyl) group than $2^o$ free radical which leads to more hyperconjugative structures thus more stability.
$2^o$ free radical will have more $\alpha -$H than $1^o$ free radical which leads to more hyperconjugative structure thus more stability. Hence correct option is (b).