Introduction of an acetyl radical (CH3CO) into the molecule of an organic compound having OH or NH2 groups. The usual reagents for this purpose are acetic anhydride or acetyl chloride. Thus, ethanol (C2H5OH) may be converted to ethyl acetate (C2H5OCOCH3). Cellulose is similarly converted to cellulose acetate by treatment with a mix containing acetic anhydride. Acetylation is commonly used to determine the number of hydroxyl groups in fats and oils.See Acetyl Value.