Question

Out of following alkenes,
(I) cis-2-butene
(II) Crans-2-butene
(III) propene
(IV) ethene.
Which is the most stable?

• A. I
• B. II
• C. III
• D. IV

Answer 1

Answer: (B)

The heat of hydrogenation of an alkene is an index of its stability. The relative rate of hydrogenation decreases with increase of steric hindrance.
Lower the heat of hydrogenation of an alkene, the more stable it is.
Trans-$2$-butene $\left(H_{\text{hyd. }}=116kJmo{l}^{-1}\right)$
is more stable than cis-$2$-butene $\left(\Delta H_{\text{hyd. }}=120kJmo{l}^{-1}\right)$
$H_{2}C=C{H}_2<C{H}_{3}CH=C{H}_2<$