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Aromatic Hydrocarbons

Aromatic Hydrocarbons

Background:


The term "aromatic" refers to organic compounds which include a benzene ring, C6H6.

Benzine consists of a circular carbon chain, or ring, which would appear to have three double carbon-carbon bonds interspersed with three single carbon-carbon bonds. In fact its chemical behaviour implies that it contains six equal bonds intermediate in nature to either the single or double bond.

Consequently the benzine ring does not take part in the normal alkene type addition reactions but more often in alkane like substitution reactions making the benzine ring a stable part of any organic compound it becomes attached to. This is the reason that aromatic chemistry has become an important subtopic within the study of organic chemistry.

Important Compounds and Derivatives:


Benzine under goes three important types of substitution reactions.

Halogenation

When benzine is exposed to a halogen in the presence of heat or UV light a substitution can take place, where one halogen ion replaces one hydrogen ion on the benzene ring. The other halogen atom then combines with the newly released hydrogen ion to form a halogen halide.

C6H6 + Br2 --> C6H5Br + HBr

Nitration

When benzene is mixed with HNO3 in the presence of sulphuric acid an NO2 group from the nitric acid can substitute with one hydrogen on the benzene ring to form nitrobenzene. That OH remaining from the nitric acid molecule then combines with the displaced hydrogen ion to form water as a residual.

C6H6 + HNO3 --> C6H5NO2 + H2O

Alkylation

When an alkyl halide is combined with bezene in the presence of a catalyst a substitution reaction can take place where the halide ion free's one hydrogen ion from the benzine ring leaveing its associated alkyl group attached in the location of the missing hydrogen ion.

C6H6 + CH3Cl --> C6H5-CH3 + HCl

This provides a means to synthesize customized aromatic compounds.

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