Question

Arrange the following free radicals in order of decreasing stability.

1. Methyl
2. Vinyl
3. Allyl
4. Benzyl

Options

• I > II > III > IV

• III > II > I > IV

• II > I > IV > III

• IV > III > I > II

Answer 1

IV > III > I > II

Explanation:

Among the alkyl free radicals, tertiary alkyl free radicals are most stable and methyl free radical is least stable.

Alkyl free radicals are less stable than benzyl and allyl free radicals, which are resonance stabilised. Due to greater conjugation, the free radical of benzoyl is more stable than that of allyl. Since the sp³ C-atom has an extra electron, the vinyl radical is the least stable.