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SolutionsReduction with Metals

1. Three reductions

Predict the result of the following reduction processes:

1-Cyclopentyl-1-butyne with H₂/Pd, with H₂ and Lindlar catalyst and with Na/liquid NH₃
H₂/Pd gives butylcyclopentane; the Lindlar catalyst, the Z alkene; and Na/NH₃, the E alkene

2. The mechanism

Why does reduction with sodium in ammonia give the trans alkene?

Because the two hydrogens are incorporated in separate steps: after the first electron and the first proton an alkenyl radical is formed, which adopts the more stable trans configuration before taking up the second electron and the second proton.

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