Question

Statement-I: The potential energy barrier for rotation about the C=C bond in 2-butene is much higher than that in ethylene.
Statement-II: Hyperconjugation effect decreases the double bond character.

• A. Statement-I is True, Statement-II is True ; Statement-II is a correct explanation for Statement-I
• B. Statement-I is True, Statement-II is True ; Statement-II is NOT a correct explanation for Statement-I
• C. Statement-I is True, Statement-II is False
• D. Statement-I is False, Statement-II is True

Answer 1

The correct option is D Statement-I is False, Statement-II is True

Internal rotation about the carbon-carbon double bond in an alkene requires breaking the bond. In $ethylene$ the hyperconjugative effects delocalize charge and stabilize the molecule. Further, it is the vicinal hyperconjugative effects that keep the molecule in the staggered conformation. Both $2-butene$ and $ethylene$ require to break almost same energy barrier for rotation of $\pi$ bond.

Hyperconjugation can be described as "double bond - no bond resonance this effect decreases the double bond character.