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Question
Which one of the following alkenes will react faster with H2 under catalytic hydrogenation condtions?
(R = Alkyl substituent)
Which one of the following alkenes will react faster with H2 under catalytic hydrogenation condtions?
(R = Alkyl substituent)
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Solution
The correct option is D
Catalytic hydrogenation of alkenes: Addition of H2 in the presence of a catalyst like Ni, Pd, Pt.
Catalytic H2 addition is a syn addition reaction. The least stable alkene will react fastest. Stability of alkene is inversely proportional to the heat of hydrogenation of alkene. Greater the number of alkyl groups attached to the doubly bonded carbon atoms, more stable is the alkene. (less reactive). So in option (d), we have two alkyl groups in cis position. So it will react fastest.
Catalytic hydrogenation of alkenes: Addition of H2 in the presence of a catalyst like Ni, Pd, Pt.
Catalytic H2 addition is a syn addition reaction. The least stable alkene will react fastest. Stability of alkene is inversely proportional to the heat of hydrogenation of alkene. Greater the number of alkyl groups attached to the doubly bonded carbon atoms, more stable is the alkene. (less reactive). So in option (d), we have two alkyl groups in cis position. So it will react fastest.
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