Hexachlorocyclohexane (HCH), C6H6Cl6, is any of several polyhalogenated organic compounds consisting of a six-carbon ring with one chlorine and one hydrogen attached to each carbon.
This structure has nine stereoisomers (eight diastereomers, one of which has two enantiomers), which differ by the stereochemistry of the individual chlorine substituents on the cyclohexane.
They have been used as models for analyzing the effects of different geometric positions of the large atoms with dipolar bonds on the stability of the cyclohexane conformation.
Common forms are: Chlorination of benzene under electrophilic aromatic substitution conditions (Cl2/FeCl3 or Cl2/AlCl3) produces chlorobenzene.
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.