1,2-Butadiene is the organic compound with the formula CH2=C=CHCH3.

It is an isomer of 1,3-butadiene, a common monomer used to make synthetic rubber.

It is a colorless flammable gas, one of the simplest substituted allenes.

[1] The C4-fraction obtained by cracking and separated by distillation consists of many compounds, predominantly (75%) 1,3-butadiene, isobutene, 1-butene.

[2] It is partially purified by extraction with N-methylpyrrolidone.