Organic Chemistry MCAT Practice Exam 2025 – The All-in-One Guide to Master Your Test Preparation!

A molecule containing one hydroxyl group (-OH) is classified as an alcohol. The presence of this functional group is the defining characteristic of alcohols, which can vary in structure and complexity, but always feature at least one hydroxyl group bonded to a carbon atom.

In the case of alcohols, the hydroxyl group contributes to properties such as increased solubility in water and the ability to participate in hydrogen bonding. These properties result from the polar nature of the O-H bond in the hydroxyl group.

The other terms listed refer to different functional groups and classes of organic compounds. Amines contain a nitrogen atom bonded to one or more alkyl or aryl groups, aldehydes have a carbonyl group (C=O) with at least one hydrogen atom directly attached to the carbon, and carboxylic acids contain a carboxyl group (-COOH), which is made up of both a carbonyl and a hydroxyl group. None of these options contain solely a hydroxyl group, which is specifically what identifies an alcohol.