Butyne

Ethylacetylene, also known as 1-butyne, but-1-yne, ethylethyne, and UN 2452, is an extremely flammable and reactive alkyne with chemical formula C₄H₆ and CAS number 107-00-6 that is used in the synthesis of organic compounds. It occurs as a colorless gas.

Dimethylacetylene (crotonylene or 2-butyne) is an alkyne with chemical formula CH₃C≡CCH₃. Produced artificially, it is a colorless, volatile, pungent liquid at standard temperature and pressure.