Hexachlorocyclohexane (HCH), , is any of several polyhalogenated
organic compound
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
chlorine
Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...
and one
hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
attached to each carbon. This structure has nine
stereoisomer
In stereochemistry, stereoisomerism, or spatial isomerism, is a form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in ...
s (eight
diastereomer
In stereochemistry, diastereomers (sometimes called diastereoisomers) are a type of stereoisomer. Diastereomers are defined as non-mirror image, non-identical stereoisomers. Hence, they occur when two or more stereoisomers of a compound have di ...
s, one of which has two
enantiomer
In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...
s), which differ by the
stereochemistry
Stereochemistry, a subdiscipline of chemistry, studies the spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereoisomers, which are defined ...
of the individual chlorine substituents on the
cyclohexane
Cyclohexane is a cycloalkane with the molecular formula . Cyclohexane is non-polar. Cyclohexane is a colourless, flammable liquid with a distinctive detergent-like odor, reminiscent of cleaning products (in which it is sometimes used). Cyclohexan ...
. It is sometimes erroneously called " benzene hexachloride" (BHC). 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
Cyclohexane conformations are any of several three-dimensional shapes adopted by cyclohexane. Because many compounds feature structurally similar six-membered rings, the structure and dynamics of cyclohexane are important prototypes of a wide r ...
. The isomers are poisonous, pesticidal, and
persistent organic pollutant
Persistent organic pollutants (POPs) are organic compounds that are resistant to degradation through chemical, biological, and photolytic processes. They are toxic and adversely affect human health and the environment around the world. Because ...
s, to varying degrees.
Hexachlorocyclohexane was dimerized to produce
mirex
Mirex is an organochloride that was commercialized as an insecticide and later banned because of its impact on the environment. This white crystalline odorless solid is a derivative of both cyclopentadiene and cubane. It was popularized to cont ...
optically active
Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circul ...
isomer
* ''beta''-hexachlorocyclohexane, β-HCH, or β-BHC (CAS RN: )
* ''gamma''-hexachlorocyclohexane, γ-HCH, γ-BHC, or lindane (CAS RN: ), the most insecticidal isomer
* ''delta''-hexachlorocyclohexane, δ-HCH, or δ-BHC (CAS RN: )
* technical hexachlorocyclohexane, t-HCH, or t-BHC (CAS RN: ), a mixture of isomers
File:(+)-alpha-hexachlorocyclohexane.svg, α-Hexachlorocyclohexane, the
dextrorotatory
Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circul ...
enantiomer
In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...
File:alpha-hexachlorocyclohexane.svg, α-Hexachlorocyclohexane, the
levorotatory
Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circul ...
benzene
Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...
under
electrophilic aromatic substitution
Electrophilic aromatic substitution (SEAr) is an organic reaction in which an atom that is attached to an aromatic ring, aromatic system (usually hydrogen) is replaced by an electrophile. Some of the most important electrophilic aromatic substitut ...
conditions (Cl2/FeCl3 or Cl2/AlCl3) produces
chlorobenzene
Chlorobenzene (abbreviated PhCl) is an aryl chloride and the simplest of the chlorobenzenes, consisting of a benzene ring substituted with one chlorine atom. Its chemical formula is C6H5Cl. This colorless, flammable liquid is a common solvent a ...
. Since mono chloro-de-hydrogenation deactivates the molecule against further electrophilic reactions, the reaction can be halted at one chlorine atom substitution.
: ''Electrophilic chlorination:'' C6H6 + Cl2 → C6H5Cl + HCl
In contrast, chlorination of benzene under
radical addition
In organic chemistry, free-radical addition is an addition reaction which involves free radicals. These reactions can happen due to the free radicals having an unpaired electron in their valence shell, making them highly reactive. Radical addi ...
conditions (Cl2, ''h''ν ( photochlorination) or Cl2, Δ, high ''P'') yields hexachlorocyclohexane isomers after three successive radical dichlorination steps.
Addition
Addition (usually signified by the Plus and minus signs#Plus sign, plus symbol, +) is one of the four basic Operation (mathematics), operations of arithmetic, the other three being subtraction, multiplication, and Division (mathematics), divis ...
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. Hence, only thrice-dichlorinated product can be isolated from this reaction.
: ''Radical addition:'' C6H6 + 3Cl2 → C6H6Cl6
Hexachlorocyclohexane isomers with more than one chlorine atom per carbon are:
*1,1,2,3,4,5-hexachlorocyclohexane
*1,1,2,3,4,6-hexachlorocyclohexane
*1,1,2,3,5,6-hexachlorocyclohexane
*1,1,2,2,3,4-hexachlorocyclohexane
*1,1,2,2,3,5-hexachlorocyclohexane
*1,1,2,2,3,6-hexachlorocyclohexane
*1,1,2,2,4,5-hexachlorocyclohexane
*1,1,2,3,3,4-hexachlorocyclohexane
*1,1,2,3,3,5-hexachlorocyclohexane
*1,1,2,3,4,4-hexachlorocyclohexane
*1,1,2,4,4,5-hexachlorocyclohexane
*1,1,2,4,4,6-hexachlorocyclohexane
*1,1,2,4,5,5-hexachlorocyclohexane
*1,1,2,5,6,6-hexachlorocyclohexane
*1,1,2,2,3,3-hexachlorocyclohexane
*1,1,2,2,4,4-hexachlorocyclohexane
*1,1,3,3,5,5-hexachlorocyclohexane