sentences:  In contrast, chlorination of benzene under radical addition conditions (Cl2, "h"ν (photochlorination) or Cl2, Δ, high "P") yields hexachlorocyclohexane isomers after three successive radical dichlorination steps.Addition rather than substitution takes place, due to the very high C–H bond dissociation energy (112 kcal/mol) that disfavors abstraction of a hydrogen atom.Addition of Cl2 destroys the aromaticity of the benzene ring, and the addition of two more Cl2 molecules is rapid compared to the first.