Question
The C—X bond in aryl halides is shorter in comparison to alkyl halides. Explain.
Solution
The electron pair present on the halogen atom resonates with the benzene ring and the following contributing structures for aryl halide are possible.
Although the charged structures (I), (II) and (III) have only little contribution towards the hybrid, yet carbon atom joined to halogen atom (X) acquires partial double bond (or sp2hybrid) character. Consequently, there is some shortening of the C—X bond length (1.69 Å) in aryl halide than in alkyl halide (1.82 Å), where there is only sp3-hybridisation and no resonance.
Although the charged structures (I), (II) and (III) have only little contribution towards the hybrid, yet carbon atom joined to halogen atom (X) acquires partial double bond (or sp2hybrid) character. Consequently, there is some shortening of the C—X bond length (1.69 Å) in aryl halide than in alkyl halide (1.82 Å), where there is only sp3-hybridisation and no resonance.
