The six π electrons are thus delocalised and can move freely about the six carbon nuclei. The delocalised π electron cloud is attracted more strongly by the nuclei of the carbon atoms than the electron cloud localized between two carbon atoms. Therefore, presence of delocalised π electrons in benzene makes it more stable.
Aromaticity:- The compounds that follow the following features are to be considered aromatic.
� Planarity � Complete delocalization of the π electrons in the ring
� Presence of( 4n + 2) π electrons in the ring where n is an integer( n = 0, 1, 2,...). This is often referred to as Hückel Rule.
Preparation of Benzene: � Cyclic polymerization of ethyne � Decarboxylation of aromatic acids
( iii) Reduction of phenol: Phenol is reduced to benzene by passing its vapours over heated zinc dust
Physical properties:
1. Aromatic hydrocarbons are non- polar molecules and are usually colourless liquids or solids with a characteristic aroma.