Question

The C-C bond length in propene is little shorter $\left(1.49A^{\circ }\right)$ than the C-C bond length $\left(1.54A^{\circ }\right)$ in ethane. This is due to:

• A. +I-effect of $C{H}_3$ group
• B. Mesomeric effect
• C. Electromeric effect
• D. Hyperconjugation effect

Answer 1

Answer: (D)

Hyperconjugation effect

$C{H}_3-C=C{H}_2$

Here, the bond length in propene is a little shorter due to the hyper-conjugation effect.

The effect is: $H^{\oplus }{CH}_2^{\ominus }-C=C{H}_2\rightleftharpoons {CH}_2=C-{CH}_2^{\ominus }$

So, here due to the hyper-conjugation effect the bond appears little shorter. But in case of ethane, there is no possibilities of hyper-conjugation.