Hexachlorocyclohexane (HCH), , is any of several polyhalogenated

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. T ...

s consisting of a six-carbon ring with one

chlorine Chlorine is a chemical element with the 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 them. Chlorine i ...

and one

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

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 enantiomers), which differ by the stereochemistry of the individual chlorine substituents on the cyclohexane. 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 In organic chemistry, cyclohexane conformations are any of several three-dimensional shapes adopted by molecules of cyclohexane. Because many compounds feature structurally similar six-membered rings, the structure and dynamics of cyclohexane ...

. The isomers are poisonous, pesticidal, and

persistent organic pollutant Persistent organic pollutants (POPs), sometimes known as "forever chemicals", are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. They are toxic chemicals that adversel ...

s, to varying degrees. Hexachlorocyclohexane was dimerized to produce

mirex Mirex was 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 cyclopentadiene. It was popularized to control fire ants b ...

, a banned pesticide. Common forms are: * ''alpha''-hexachlorocyclohexane, α-HCH, or α-BHC (

CAS RN A CAS Registry Number (also referred to as CAS RN or informally CAS Number) is a unique identifier, unique identification number assigned by the Chemical Abstracts Service (CAS), US to every chemical substance described in the open scientific li ...

: ), the optically active isomer * ''beta''-hexachlorocyclohexane, β-HCH, or β-BHC (CAS RN: ) * ''gamma''-hexachlorocyclohexane, γ-HCH, γ-BHC, or

lindane Lindane, also known as ''gamma''-hexachlorocyclohexane (γ-HCH), gammaxene, Gammallin and benzene hexachloride (BHC), is an organochlorine chemical and an isomer of hexachlorocyclohexane that has been used both as an agricultural insecticide and ...

(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 α-Hexachlorocyclohexane (α-HCH) is an organochloride which is one of the isomers of hexachlorocyclohexane (HCH).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 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 ...

enantiomer File:beta-hexachlorocyclohexane.svg,

β-Hexachlorocyclohexane β-Hexachlorocyclohexane (β-HCH) is an organochloride which is one of the isomers of hexachlorocyclohexane (HCH).lindane Lindane, also known as ''gamma''-hexachlorocyclohexane (γ-HCH), gammaxene, Gammallin and benzene hexachloride (BHC), is an organochlorine chemical and an isomer of hexachlorocyclohexane that has been used both as an agricultural insecticide and ...

File:delta-hexachlorocyclohexane.svg, δ-Hexachlorocyclohexane File:epsilon-hexachlorocyclohexane.svg, ε-Hexachlorocyclohexane File:zeta-hexachlorocyclohexane.svg, ζ-Hexachlorocyclohexane File:eta-hexachlorocyclohexane.svg, η-Hexachlorocyclohexane File:theta-hexachlorocyclohexane.svg, θ-Hexachlorocyclohexane Chlorination of

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...

under

electrophilic aromatic substitution Electrophilic aromatic substitution is an organic reaction in which an atom that is attached to an aromatic system (usually hydrogen) is replaced by an electrophile. Some of the most important electrophilic aromatic substitutions are aromatic n ...

conditions (Cl₂/FeCl₃ or Cl₂/AlCl₃) produces

chlorobenzene Chlorobenzene is an aromatic organic compound with the chemical formula C6H5Cl. This colorless, flammable liquid is a common solvent and a widely used intermediate in the manufacture of other chemicals. Uses Historical The major use of chlorob ...

. 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. The addition may occur between a radical and a non-radical, or between two radicals. The basic steps with examples of the free-radical addition ( ...

conditions (Cl₂, ''h''ν (

photochlorination Photochlorination is a chlorination reaction that is initiated by light. Usually a C-H bond is converted to a C-Cl bond. Photochlorination is carried out on an industrial scale. The process is exothermic and proceeds as a chain reaction initiated ...

) 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. 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 *1,1,3,3,5,5-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

References

External links

Hexachlorocyclohexane (HCH)
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