Question

The alkyl radical with most stability is:

• A. ethyl radical
• B. methyl radical
• C. $2^0$ - butyl radical
• D. $3^0$ - butyl radical

Answer 1

Answer: (D)

$3^0$ - butyl radical

The stability order of alkyl free radical is $M{e}_3{C}^{\ast }>M{e}_2{C}^{\ast }H>Me{C}^{\ast }H2>C{H}_3^{\ast }$.

This is due to hyperconjugation or no bond resonance of adjacent hydrogens with the positive charge. Tertiary free radical like $3^{o}Butyl$ has 3 methyl groups with 9 hyperconjugative hydrogens which makes it most stable.