Homolysis (chemistry)

In chemistry, homolysis (from Greek ὅμοιος (homoios) 'equal' and λύσις (lusis) 'loosening') or homolytic fission is the dissociation of a molecular bond by a process where each of the fragments (an atom or molecule) retains one of the originally bonded electrons.

During homolytic fission of a neutral molecule with an even number of electrons, two radicals will be generated.

[2] BDE is defined as the "enthalpy (per mole) required to break a given bond of some specific molecular entity by homolysis," symbolized as D.[3] BDE is dependent on the strength of the bond, which is determined by factors relating to the stability of the resulting radical species.

Because of the relatively high energy required to break bonds in this manner, homolysis occurs primarily under certain circumstances: Adenosylcobalamin is the cofactor which creates the deoxyadenosyl radical by homolytic cleavage of a cobalt-carbon bond in reactions catalysed by methylmalonyl-CoA mutase, isobutyryl-CoA mutase and related enzymes.

This triggers rearrangement reactions in the carbon framework of the substrates on which the enzymes act.

The O-O σ bond in dibenzoyl peroxide is cleaved homolytically, distributing a radical to each benzoyloxy.
The bond dissociation energy depends on the electronegativity of the species bonded.
An sp3 hybridized atom is the most stable configuration for a radical because of the low s-character.
This bromine dioxide radical is stabilized by the resonance of the molecule. Structure from J. Chem. Phys. (1997) 107, 8292-8302. [ 7 ]
The most substituted carbon radical is the most stable.