Question

Sort the radicals below from most stable to least stable.

Short answer

The order of radical stability is: 1 > 3 > 2

Step-by-step solution

 Step 1: Free radical

These molecular species have at least one unpaired electron. Molecules normally consist of pairs of electrons.These are electron-deficient species.

Stability of free radical

• As radicals are electron-deficient species. Their stability Increases with a number of alkyl groups present on carbon-bearing the free radical. So, radical stability increases in the order vinyl < methyl < primary < secondary < tertiary < allyl radical.
• Radicals Are Stabilized by resonance

Stability of radical 1

RADICAL 1

It is an allyl radical so most stable. Due to resonance this radical is stabilized making it most stable among all given radicals.

Stability of radical 2

RADICAL 2

It is a vinyl radical so least stable. As we know alkene group does not donate electron instead it tries to take electron so it makes radical even more unstable.

Stability of radical 3

RADICAL 3

It is secondary radical so less stable as here only two alkyl groups are present to donate electron to radical which is electron deficient.

Order of radical from most stable to least stable

The order of radical stability is: 1 > 3 > 2

This order is given based on presence of resonance in 1, presence of two electron donating group in 2 and an electron withdrawing alkene group in three.