Name: Estimation of Carbon and Hydrogen
Uploaded: 2019-07-19
Duration: 4 min 27 s
Description: Liebig's method helps estimate carbon and hydrogen in organic compounds. In this method, the compound carbon and hydrogen are converted into CO2 and H2O, res...

Question

Comment upon the statement that the usual order of inductive effects of alkyl groups is generally reversed when attached to a double bond or benzene ring. Name the involved electronic effect and illustrate your answer with suitable examples.

Accepted Answer

Alkyl groups behave differently when attached to benzene ring and carbon-carbon double bond. This is because, the electron release occurs through hyperconjugation.

Each C-H sigma bond participates in delocalization and increases the negative charge density in benzene ring or carbon-carbon double bond. More the number of C-H bonds, more is the number of contributing structures and thus higher the electron releasing effect of alkyl group.

For example, the number of contributing structures in methylbenzene, ethylbenzene, isopropylbenzene and tertiary butylbenzene are $9, 6, 3$ and $0$ respectively. Thus, the electron releasing effect of methyl group is maximum and that of tertiary butyl group is minimum.

Comment upon the statement that the usual order of inductive effects of alkyl groups is generally reversed when attached to a double bond or benzene ring. Name the involved electronic effect and illustrate your answer with suitable examples.

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