alkenyl

Alkenyl is a term in organic chemistry used to describe a hydrocarbon substituent that contains a carbon–carbon double bond and is derived from an alkene by removal of one hydrogen atom. The alkenyl group is attached to a parent molecule at the site where the hydrogen was removed. In general, an alkenyl substituent has the formula CnH2n−1 for an n-carbon chain.

Nomenclature for alkenyl groups follows the same logic as the parent alkenes, with the suffix -yl indicating substitution. For example, ethenyl is the systematic name for the vinyl group, and prop-2-en-1-yl corresponds to the allyl group. Common names such as vinyl (ethenyl) and allyl (prop-2-en-1-yl) are widely used in practice.

Reactivity and properties of alkenyl groups are largely governed by the carbon–carbon double bond. They participate in addition reactions, radical processes, and are key players in polymerization, especially in vinyl polymers. Alkenyl substituents can also participate in cross-linking and various carbon–carbon bond-forming reactions that leverage the C=C bond.

Relation to other substituents: alkenyl groups are contrasted with alkyl groups, which are saturated and lack double bonds, and with aryl groups, which are derived from aromatic rings. The alkenyl designation is useful in describing substituent patterns in compounds that retain an alkene moiety, and it is widely used in synthetic planning and structural description.