Why are allylic and benzylic radicals always more stable?

1 Answer
Jul 25, 2015

Benzylic and allylic radicals are more stable because they are stabilized by resonance.


Resonance involves a delocalization of electron density, and any process that delocalize electrons lowers the energy of a system.

(from www.mhhe.com)

We can write two equivalent resonance structures for the allyl radical, so its energy is lower than that of, say, a propyl radical.

The resonance energy of the allyl radical is about 45 kJ/mol.

The benzyl radical has even more resonance structures.

(from chemistry.stackexchange.com)

Its resonance energy is about 100 kJ/mol.