Given below are two statements : Statement I : Hyperconjugation is a permanent effect. Statement II : Hyperconjugation in ethyl cation \( (\mathrm{CH_3-CH_2^+}) \) involves the overlapping of \( \mathrm{C_{sp^2}-H_{1s}} \) bond with empty \( 2p \) orbital of the other carbon. Choose the correct option :
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Hyperconjugation involves the delocalization of $\sigma$-electrons from a C-H bond into an adjacent empty p-orbital or $\pi$-system. Remember, the C-H bond must be on an sp³-hybridized carbon adjacent to an sp²-hybridized carbon.
Let's evaluate each statement.
Statement I: Hyperconjugation is a permanent effect. This is true. Like the inductive effect and resonance, hyperconjugation involves a permanent delocalization of sigma \( (\sigma) \) electrons, which influences the properties of the molecule at all times. It is not a temporary effect that only occurs in the presence of a reagent.
Statement II: Hyperconjugation in ethyl cation \( (\mathrm{CH_3-CH_2^+}) \) involves the overlapping of \( \mathrm{C_{sp^2}-H_{1s}} \) bond with empty \( 2p \) orbital of other carbon.
Let's analyze the structure of the ethyl cation: \( \mathrm{H_3C^\beta-C^\alpha H_2^+} \).
The positively charged carbon \( (\mathrm{C^\alpha}) \) is \( sp^2 \)-hybridized and has an empty \( 2p \) orbital.
The adjacent carbon \( (\mathrm{C^\beta}) \) is \( sp^3 \)-hybridized.
Hyperconjugation occurs by the overlap of the \( \mathrm{C^\beta-H} \) sigma bond (which is a \( \mathrm{C_{sp^3}-H_{1s}} \) bond) with the adjacent empty \( 2p \) orbital of the \( \mathrm{C^\alpha} \) carbocation.
The statement incorrectly says the overlap is with a \( \mathrm{C_{sp^2}-H_{1s}} \) bond. Therefore, Statement II is false.
Since Statement I is correct and Statement II is false, the correct option is (C).
