In chemistry, vinylene (also ethenylene or 1,2-ethenediyl)[1] is a divalent functional group (a part of a molecule)[2] with formula −CH=CH−;[3] namely, two carbons, each connected to the other by a double bond, to an hydrogen atom by a single bond, and to the rest of the molecule by another single bond.
[4][5] This group can be viewed as a molecule of ethene (ethylene, H2C=CH2) with an hydrogen removed from each carbon; or a vinyl group −CH=CH2 with one hydrogen removed from the terminal carbon.
[6][7][8] It should not be confused with the vinylidene group =C=CH2 or >C=CH2.
A vinylene unit attached to two distinct atoms other than hydrogen (namely R−CH=CH−R') is a source of cis-trans isomerism.
[9][10] The vinylene group is the repeating unit in polyacetylene and in polyenes.