Hydrogenation of an Alkyne to a (E)-Alkene (trans-alkene)

Alkynes can be reduced to trans-alkenes with the use of sodium dissolved in an ammonia solvent. An Na radical donates an electron to one of the P bonds in a carbon-carbon triple bond. This forms an anion, which can be protonated by a hydrogen in an ammonia solvent. This prompts another Na radical to donate an electron to the second P orbital. Soon after this anion is also protonated by a hydrogen from the ammonia solvent, resulting in a trans-alkene.

R-C≡C-R + 2 Na in NH₃ (liq) ——> trans R-CH=CH-R + 2 NaNH₂