An alcohol is an organic compound containing a hydroxyl (-OH) group. In the IUPAC nomenclature system, the suffix “-ol” is used in the name of each alcohol. The simplest alcohol is methanol (methyl alcohol, CH3OH), and the most commonly encountered alcohol is ethanol (ethyl alcohol, C2H5OH) which is contained in alcoholic beverages. Alcohols with three or more carbons have isomers: Propyl alcohol has two isomers, which are propan-1-ol (CH3CH2CH2OH) and propan-2-ol (CH3CH(OH)CH2). Many low-molecular-weight alcohols, such as ethanol and propan-2-ol, are used as disinfectants, since they diffuse easily through cell membranes and denaturize proteins. Compounds whose hydroxyl group is connected to benzene ring are referred to as phenols.