Question

What are the limitations of the KeKule Structure?

Answer 1

Hint : With the ability of mankind to detect the actual structure of a molecule, everybody was interested in viewing the actual structure of the aromatic complexes like the benzene. The structure was observed but with a confusion regarding the motion of electrons in the ring. Several structures were proposed, some of them are Kekule structure, Dewar structure, Claus structure, Baeyer structure, and many more.

Complete Step By Step Answer:
The limitations of kekule structure are as follows: -
(i). According to kekule’s structure, there should be at least two different structures of the $1,2$ -dibromobenzene. But in actuality there is only one structure of $1,2$ -dibromobenzene is found to exist.
(ii). According to kekule’s structure, benzene is a cyclohexene with three double bonds alternate to one another, thus the benzene is alkene. But it was found to be that the benzene ring is more stable than alkene and never acts as an alkene in any reaction. Further benzene is more stable than alkenes because of conjugation.
(iii). As the benzene is found to be a cycloalkene, thus it was believed that this will undergo addition reactions like other alkenes go, but however it was found experimentally that benzene undergoes substitution rather than addition reaction easily.
(iv). Due to the conjugation the bond length of single and double bonds are not equal to the calculated values. The double bond acquires partial single bond characters and single bond acquires partial double characters, thus the bond length lies in between the actual values of the single and double bond.

Note :
The Kekule structure, with few limitations, are widely accepted throughout the world of chemistry. It was in $1865$ that the ring structure with alternate double bonds was proposed by Friedrich August Kekule Von Stradonitz commonly called the kekule, a German Scientist. Due to the importance of benzene in organic chemistry, today kekule is considered as one of the founders of modern day organic chemistry.