What is the prefix used in organic nomenclature to denote the hydroxyl group?

• A. Hydroxy
• B. Amino
• C. Methyl
• D. Ethyl

Answer: (A)

Hydroxyl groups are indicated in systematic naming by the prefix hydroxy-. This shows that an -OH is attached to the carbon framework. If the hydroxyl is the main functional group, the -ol suffix is used (for example, ethanol is propan-1-ol), but when the OH is a substituent or another group takes priority, we attach hydroxy- as a prefix to the rest of the name. For instance, hydroxybenzene names a benzene ring with an OH substituent (the common name is phenol), and 2-hydroxypropane illustrates OH as a substituent on a propane skeleton. The other options denote different groups or substituents: amino- indicates an amino group, while methyl- and ethyl denote alkyl substituents.