Question

What are arenes? How are they classified? Discuss briefly isomerism and nomenclature of arenes?

Answer 1

Hint: As we know that the arenes are aromatic hydrocarbons. The term "aromatic" originally referred to their pleasant smells but now implies a particular sort of delocalized bonding. Aromatic hydrocarbons or sometimes called arenes or aryl hydrocarbon are hydrocarbons with sigma bonds and delocalized \[\pi \] electrons between carbon atoms forming rings.

Complete answer:
Arenes are aromatic hydrocarbons. They are classified into three classes depending upon the number of fused benzene rings. The fusion of benzene rings can be Monocyclic, Polycyclic and linear fusion of benzene rings. Monocyclic arenes can be toluene, ethyl benzene that have only a single benzene ring. The other class is polycyclic that has more than one fused ring of benzene for example: biphenyl, stilbene. The last classification is linear fusion of aromatic rings that includes naphthalene, anthracene. Arenes show position isomerism. Benzene is a symmetrical molecule; it has six hydrogen atoms that are equivalent. When we replace one hydrogen atom and in its place substitute it with another group leads to the formation of arenes. The mono substitution of benzene does not show isomerism. And when two hydrogen atoms are replaced and substituted with different atoms or groups, the three isomers Ortho, Para and Meta are formed. And like this if we increase the substitution on benzene rings, isomers also increase.

Note:
We have to know that the arenes you are likely to meet at this level are based on benzene rings. The simplest of them is benzene itself, \[{C_6}{H_6}\]. The next simplest is methylbenzene which is also known as toluene and has one of the hydrogen atoms attached to the ring replaced by a methyl group - \[{C_6}{H_5}C{H_3}\].