Acyl is an organic radical (or functional group) obtained from an organic acid by the removal of the carboxylic hydroxyl group. Acyl groups can be written as having the general formula -COR, where there is a double bond between the carbon and oxygen. The names of acyl groups typically end in -yl, such as formyl, propyl, benzoyl. Acyl groups can be used in Friedel-Crafts acylation.