to aromatic compounds as discussed below: ( . ) Problem . How will you convert ethanoic acid into benzene? .
Aromatic Hydrocarbon These hydrocarbons are also known as ‘ arenes ’. Since most of them possess pleasant odour ( Greek; aroma meaning pleasant smelling ), the class of compounds was named as ‘ aromatic compounds ’. Most of such compounds were found to contain benzene ring. Benzene ring is highly unsaturated but in a majority of reactions of aromatic compounds, the unsaturation of benzene ring is retained.
However, there are examples of aromatic hydrocarbons which do not contain a benzene ring but instead contain other highly unsaturated ring. Aromatic compounds containing benzene ring are known as benzenoids and those not containing a benzene ring are known as non-benzenoids . Some examples of arenes are given below: Benzene Toluene Naphthalene Biphenyl . .
Nomenclature and Isomerism The nomenclature and isomerism of aromatic hydrocarbons has already been discussed in Unit . All six hydrogen atoms in benzene are equivalent; so it forms one and only one type of monosubstituted product. When two hydrogen atoms in benzene are replaced by two similar or different monovalent atoms or groups, three different position isomers are possible. The , or , is known as the ortho ( o –), the , or , as meta ( m –) and the , as para ( p –) disubstituted compounds.
A few examples of derivatives of benzene are given below: Methylbenzene , -Dimethylbenzene (Toluene) ( o -Xylene) , Dimethylbenzene , -Dimethylbenzene ( m -Xylene) ( p -Xylene) . . Structure of Benzene Benzene was isolated by Michael Faraday in . The molecular formula of benzene, C H , indicates a high degree of unsaturation.
This molecular formula did not account for its relationship to corresponding alkanes, alkenes and alkynes which you have studied in earlier sections of this unit. What do you think about its possible structure? Due to its unique properties and unusual stability, it took several years to assign its structure. Benzene was found to be a stable molecule and found to form a