What functional group does an alcohol contain?
Shown here are two well-known alcohols, the first being the one-carbon-atom alcohol, commonly known as methyl alcohol, which has the IUPAC name methanol, and the second being the three-carbon-atom alcohol with the common name isopropyl alcohol and the IUPAC name propan-2-ol. To answer the question, we need to determine what functional group each of these alcohols contain.
A functional group is defined as a part of a molecule made of particular atoms or ions in a particular bonding arrangement that usually behaves in specific predictable ways. And an alcohol is defined as an organic compound that contains a hydroxy functional group, signified by the chemical formula OH, that is covalently bonded to a saturated carbon atom or a carbon atom that is only singly bonded to other carbon and/or hydrogen atoms. While their carbon chain lengths differ, both contain a hydroxy group, or an OH group, covalently bonded to a saturated carbon atom, which classifies them as alcohols.
To continue the discussion, let’s take a look at another one-carbon-atom organic molecule with the common name formic acid and the IUPAC name methanoic acid. A quick glance might lead one to believe that the presence of the hydroxy group in both molecules would indicate both should be classified as alcohols. However, the hydroxy group in methanoic acid is part of a different and bigger functional group called a carboxyl group, classifying methanoic acid not as an alcohol but as a carboxylic acid, which is defined as an organic compound that contains a carboxyl group, signified by the chemical formula COOH.
More specifically, it consists of a carbonyl group signified by the C double bond O, which is singly bonded through the carbon atom to a hydroxy group, indicated by the letters OH. The presence of the double bond indicates the carbon atom covalently bonded to the hydroxy group in methanoic acid is an unsaturated carbon atom. Since the hydroxy group in methanoic acid is not covalently bonded to a saturated carbon atom, this molecule is not classified as an alcohol. Therefore, what functional group does an alcohol contain? The answer is an OH group.