Question

Identify the alkene with the highest value of heat of hydrogenation:

• A. propene
• B. $2$-methylpropene
• C. cis-$2$-pentene
• D. $2$-methyl-$2$-butene

Answer 1

The correct option is A propene

Heat of hydrogenation of alkenes is a measure of the stability of carbon-carbon double bonds. All else being the same, the smaller the numerical value of heat of hydrogenation of an alkene, the more stable the double bond therein.

Based on heats of hydrogenation of alkenes, the trend in the stability of carbon-carbon double bonds is tetrasubstituted > trisubstituted > disubstituted > monosubstituted > unsubstituted.

So higher the stability, lower the heat of hydrogenation

Hence, highest heat of hydrogenation will be of the unsubstituted alkene.

In this case it is propene.

Hence, option A will be correct