Rank the following radicals in decreasing order of stability. Classify each as primary, secondary, or tertiary.

(a)

(b)

(c)

(d)

An atom or group of atoms containing odd or unpaired electron is known as the free radical. The unpaired electron is represented by a single unpaired dot in the formula. Free radicals are electrically neutral. They are highly reactive species formed by homolytic fission of a covalent bond.

Tertiary alkyl radical is more stable than secondary alkyl radical which in turn is more stable than primary alkyl radical. However, methyl free radical which does not contain any alkyl group is the least stable.

Tertiary allylic radical is the most stable than tertiary since it is stabilized by resonance while the primary radical is the least stable.

radicals in order from most stable to least stable

Resonance delocalization is particularly effective in stabilizing a radical.

tertiary allylic radical stabilized by resonance