Hydrocarbons Ques 22

22. Which one of the following alkenes will react faster with $H_2$ under catalytic hydrogenation conditions?

[2005] (a)

(b)

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Solution:

  1. (a) Option (a) and (b) are more stable due to more hyperconjugated $(6 \alpha-H)$ hydrogen atoms cis-2-butene (option a) is less hindered that 2methyl propene (option b).

Thus, hydrogenation will be fastest for cis-2butene.

As catalytic hydrogenation happens on the surface of catalysis on the some side of molecule therefore the rate of catalytic hydrogenation depends on stability of alkene and steric hindrance on the molecule.