Hexachlorocyclohexane

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Hexachlorocyclohexane (HCH), C
6
H
6
Cl
6
, 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. 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. [1] The isomers are poisonous, pesticidal, and persistent organic pollutants, to varying degrees.

Hexachlorocyclohexane was dimerized to produce mirex, a banned pesticide.

Common forms are:

Chlorination of benzene under electrophilic aromatic substitution conditions (Cl2/FeCl3 or Cl2/AlCl3) produces chlorobenzene. 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 conditions (Cl2, hν (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. 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:

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<span class="mw-page-title-main">Lindane</span> Organochlorine chemical and an isomer of hexachlorocyclohexane

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β-Hexachlorocyclohexane Chemical compound

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α-Hexachlorocyclohexane Chemical compound

α-Hexachlorocyclohexane (α-HCH) is an organochloride which is one of the isomers of hexachlorocyclohexane (HCH). It is a byproduct of the production of the insecticide lindane (γ-HCH) and it is typically still contained in commercial grade lindane used as insecticide. Lindane, however, has not been produced or used in the United States for more than 20 years. At ambient temperatures it is a stable, white, powdery solid substance. As of 2009, the Stockholm Convention on Persistent Organic Pollutants classified (α-HCH) and (β-HCH) as persistent organic pollutants (POPs), due to the chemical's ability to persistence in the environment, bioaccumulative, biomagnifying, and long-range transport capacity.

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1,2,3,4-Cyclohexanetetrol (also named cyclohexane-1,2,3,4-tetrol, 1,2,3,4-tetrahydroxycyclohexane, or ortho-cyclohexanetetrol) is an organic compound whose molecule can be described as a cyclohexane with four hydroxyl (OH) groups substituted for hydrogen atoms on four consecutive carbon atoms. Its formula can be written C
6
H
12
O
4
, C
6
H
8
(OH)
4
, or (–CH(OH)–)4(–CH
2
–)2.

<span class="mw-page-title-main">1,2,4,5-Cyclohexanetetrol</span> Chemical compound

1,2,4,5-Cyclohexanetetrol (also named cyclohexane-1,2,4,5-tetrol, 1,2,4,5-tetrahydroxycyclohexane, or para-cyclohexanetetrol) is an organic compound whose molecule can be described as a cyclohexane with four hydroxyl (OH) groups substituted for hydrogen atoms on two non-adjacent pairs of adjacent carbon atoms. Its formula can be written C
6
H
12
O
4
, C
6
H
8
(OH)
4
, or [–(CH(OH)–)2CH
2
–]2.

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Negative hyperconjugation is a theorized phenomenon in organosilicon compounds, in which hyperconjugation stabilizes or destabilizes certain accumulations of positive charge. The phenomenon explains corresponding peculiarities in the stereochemistry and rate of hydrolysis.

References

  1. Zdravkovski, Zoran (2004). "Theoretical Study of the Stability of Hexachloro- and Hexafluorocyclohexane Isomers" (PDF). Bulletin of the Chemists and Technologists of Macedonia. 23 (2): 131–137. Archived from the original (PDF) on 2005-12-28. Retrieved 2016-04-17.