Polynuclear Aromatic Hydrocarbons
Polynuclear aromatic hydrocarbon is an arrangement of more than one aromatic ring in the molecule. Depending upon the mode of attachment of various rings, the polynuclear aromatic hydrocarbons may be classified into two classes:
1. Isolated Benzenoid Hydrocarbons
2. Condensed or Fused Benzenoid Hydrocarbons
Isolated Benzenoid Hydrocarbons
In isolated benzenoid hydrocarbon, two or more rings are joined together directly or through carbon chain. Biphenyl, diphenylmethane and triphenylmethane are the examples of isolated benzenoid hydrocarbon.
Condensed or Fused Benzenoid Hydrocarbon
In condensed or fused benzenoid hydrocarbons, two or more benzene rings are fused together in such a way that each pair of rings shares two carbons. Naphthalene, anthracene, phenanthrene etc. are the example of condensed or fused benzenoid hydrocarbons.
