Question

Which one of the following alkenes will react faster with H₂ under catalytic hydrogenation conditions?(R=Alkyl substituent)

• A.
• B.
• C.
• D.

Answer 1

The Correct Option is A

The hydrogens are transported from the catalyst to the same side of the double bond during catalytic hydrogenation, resulting in cis-alkenes. It stands to reason that the less R substituents there are, the less steric interference there is, and the faster the rate of hydrogenation.
Alkene stability is negatively correlated with alkene hydrogenation heat.
In the third compound, hydrogenation is catalytically accomplished. In the third compound more than any other compound, less energy is needed to break the double bond.
The alkene is more stable the more alkyl groups there are connected to the doubly bound carbon atoms. (Less aggressive)