oyl

Oy l is a suffix used in organic chemistry to denote an acyl substituent, the carbonyl-containing fragment R-CO attached to another group. The -oyl ending signals that the group is derived from a carboxylic acid by removal of the hydroxyl group, forming a carbonyl-linked moiety.

Common examples include formyl (H-CO-), acetyl or ethanoyl (CH3-CO-), propanoyl (CH3CH2-CO-), and benzoyl (C6H5-CO-). In systematic naming, these may be called formyl, ethanoyl, propanoyl, and benzoyl groups, with exact forms depending on the preferred nomenclature. The term is widely used when describing the acyl portion of larger structures such as esters, amides, and anhydrides.

Usage and significance: The acyl group is formed by removing the hydroxyl from a carboxylic acid, yielding R-CO-. This moiety can be transferred to other molecules in reactions known as acylation, utilizing reagents such as acyl chlorides, anhydrides, or activated derivatives. The presence of the carbonyl carbon in the -oyl group influences reactivity and selectivity in many organic transformations.

Relation to other terms: The -oyl suffix distinguishes acyl substituents from the -yl suffix, which denotes hydrocarbon substituents lacking a carbonyl group. Understanding whether a fragment is -oyl or -yl helps in naming and in predicting reaction behavior, particularly in esterification, amidation, and acyl transfer processes.

See also: acyl group; acylation; ester; amide; acid chloride; carboxylic acid.