Question

Question: Which alkene in each pair has the larger Heat of hydrogenation?

a.

b.

Short answer

Answer

a.

b.

Step-by-step solution

Heat of hydrogenation

When (C=C) is broken and new (C-H) are formed, some energy is released out, known as the heat of hydrogenation.

The stability of alkenes is inversely proportional to the heat of hydrogenation.

Stability of alkenes

One of the factors that affect the stability of alkenes is substituents. The number of substituents and their position defines the stability of alkenes.

Determination of alkenes with larger heat of hydrogenation

a. Cis alkenes are less stable than trans alkenes due to steric hindrance; therefore, cis alkenes will have larger heat of hydrogenation.

Cis and trans alkene

b. As the number of substitutions increases, the stability increases as hyperconjugation increases.

Di and Tri substituted alkene