But-2-yne

Overview

A symmetrical internal alkyne linking partial reduction with alkene stereochemistry.

Neither triple-bond carbon has a terminal hydrogen. Controlled catalytic reduction and dissolving-metal reduction lead to different but-2-ene geometries: cis and trans, respectively. Further hydrogenation removes the double bond, so stopping at the alkene requires a suitable reaction system.

Identifiers

Formula

C4H6

Molar mass

54.09 g/mol

Also known as

Dimethylacetylene, 4-butyne, but-4-yne, RefChem:86060, 2-BUTYNE, Crotonylene

Related compounds

• Alkynes

  But-2-yne is a specific member of the alkynes family.

Connected reactions

• Partial hydrogenation: But-2-yne → cis-But-2-ene

  The alkyne binds to the catalyst surface and receives both hydrogen atoms from the same face. This syn addition gives cis-but-2-ene; the deactivated Lindlar catalyst helps limit further reduction to butane.

• Dissolving metal reduction: But-2-yne → trans-But-2-ene

  Successive electron transfers and protonations convert the triple bond into a double bond. The intermediate sequence favours the less crowded arrangement that gives trans-but-2-ene, so this is not the same process as hydrogen delivery on a metal surface.

References

1. PubChem Compound Summary: But-2-yne (CID 10419)National Center for Biotechnology Information · PubChem

   Identity, molecular formula, molecular weight and aliases retrieved via PUG REST on 2026-09-08.

2. OpenStax Organic Chemistry: Reduction of alkynesJohn McMurry · OpenStax · 2023

   Supports the qualitative structure and reactivity context; identity and numerical measurements retain their original references.

3. OpenStax Organic Chemistry: Alkyne acidity: formation of acetylide anionsJohn McMurry · OpenStax · 2023

   Supports the qualitative structure and reactivity context; identity and numerical measurements retain their original references.