1,2-Dibromoethylene

1,2-Dibromoethylene, also known as 1,2-dibromoethene and acetylene dibromide, is a dihalogenated unsaturated compound with one bromine on each of the two carbon atoms. There are two isomers of this compound, cis and trans. Both isomers are colorless liquids.

Synthesis
1,2-Dibromoethylene can be synthesized by halogenation of acetylene (C$3$H$2$) with bromine (Br$2$). In order to prevent the formation of tetrahalogenated compounds, acetylene is used in excess, with Br$2$ as the limiting reagent.
 * [[Image:Bromination of acetylene.svg|400px|Bromination of acetylene]]

Alternately, halogenation of this kind could also be achieved through the use of two equivalents of N-bromosuccinimide and lithium bromide (LiBr). N-Bromosuccinimide provides Br$2$ as an electrophile, which is followed by Br$+$ from LiBr.


 * [[Image:HalogenationLiBrNBS.png|400px]]