Question

Among the following alkenes,
$\underset{I}{\text{1-butene}}\underset{II}{\text{cis-2-butene}}\underset{III}{\text{trans-2-butene}}$
the decreasing order of stability is

• A. II > I > III
• B. III > II > I
• C. III > I > II
• D. I > II > III

Answer 1

Answer: (B)

Stability of alkene $\propto \frac{1}{\text{Heat of hydrogenation of alkene}}$
Stability of an alkene depends upon the heat of hydrogenation of an alkene. Therefore, the lower the heat of hydrogenation of an alkene, higher will be stability.
Order of stability is
trans-$2$-butene > cis-$2$-butene $>1-$ butene.
Heat of hydrogenation (kJ/mol) are $115.5,119.6$ and $126.8$ respectively.