Q10-34E-b - 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: 1 > 3 > 2

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 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

Step 3: 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.

Step 4: 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.

Step 5: 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.

Step 6: 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.