Chapter 21, Problem 90A

Interpretation Introduction

Interpretation:

The Kekulé’s structure of benzene needs to be drawn and the reason why this doesn’t represent actual structure needs to be explained.

Concept introduction:

Benzene is an aromatic compound with 6 carbon attached to each other in cyclic hexagonal ring. Each carbon is attached to 1 hydrogen by single bond and one carbon with double bond on one side and single bond on other side.

Explanation of Solution

A sensible structure of benzene was proposed by Kekulé. According to him, the carbons are arranged in hexagon with alternate single and double bonds present between them. Each carbon is attached to one hydrogen atom via single bond. The proposed structure of Kekulé is:

It does not represent correct structure of benzene as:

• It suggests two different type of carbon-carbon bonds in benzene that is, single and double carbon-carbon bond but in benzene all the bonds are exactly same and benzene is planar molecule.
• Due to presence of three double bond, it can be expected that benzene undergoes addition reaction as those of alkenes. But benzene rarely undergoes addition reaction whereas it undergoes substitution reactions.
• The real structure of benzene is very stable in comparison to the structure of benzene proposed by Kekulé.