Esters are carboxylic acid derivatives in which the hydroxyl hydrogen has been replaced by a hydrocarbon group. Esters can be seen as the products of condensation between a carboxylic acid and an alcohol: R-CO-OH + HO-R' ---(-water)---> R-CO-O-R'. Esters of acetic acid are acetates. The identity of the alocohol group R' is specified as a prefix.