Diacetylene (also known as butadiyne), with the formula C₄H₂, is a highly unsaturated hydrocarbon that contains three single bonds and two triple bonds. It is the first in the series of polyynes. The trivial name "diacetylene" refers to the two C-C triple bonds and the possible formation from acetylene (see below). It does not mean that diacetylene is the formal dimer of acetylene, what is rather true for butenyne or cyclobutadiene.