Is BDE a measure of free radical stability?

1 Answer
Jan 2, 2015

Yes, BDE is a measure of free radical stability.

BDE is a measure of the energy required to break a bond and form free radicals.

A free radical is an electron-deficient species. A radical that can best accommodate this deficiency will be the most stable.

As free radicals become more stable, their BDEs decrease. So, BDE is a measure of free radical stability.

Let’s look at some of the trends.

Stability increases in the order CH₃ < 1° < 2° < 3°

Alkyl groups are electron donating. A 3° radical is the most stable because it has the most alkyl groups.

The C-H BDE decreases as we go from methane to 2-methylpropane because the radicals are becoming more stable.

Free radicals are stabilized by resonance.

The BDE of propene is less than that of methane, because the allylic radical is stabilized by resonance.

The stability of free radicals decreases from left to right in the Periodic Table.

As we move from left to right, the atoms become more electronegative and less able to stabilize an electron deficiency.

Here's a video on BDEs and radical stability trends.