Q10-34E-c - Organic Chemistry (Mcmurry)

Question

Sort the radicals below from most stable to least stable.

Step-by-Step Solution

Answer

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

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.

Step 2: Stability of free radical

• As radicals are electron deficient species. Their stability Increases with 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

Step 3: Stability of radical 1

RADICAL 1

It is a secondary radical so less stable, as mentioned earlier more the alkyl groups attached more will be the stability. Here only two alkyl groups are present.

Step 4: Stability of radical 2

RADICAL 2

It is a tertiary radical so most stable. Here three alkyl groups are present making it most stable among given radicals.

Step 5: Stability of radical 3

RADICAL 3

It is primary radical so least stable. Here only a single alkyl group is attached to radical making it least stable among all.

Step 6: Order of radical from most stable to least stable

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

This order is given based on the presence of number of alkyl group. More the number of alkyl group more will be its stability.