Functional Groups Definition and Examples

Chemistry Glossary Definition of Functional Groups

Benzyl acetate has an ester group (red).
Benzyl acetate has an ester group (red). Wikimedia Commons/Public Domain

Functional Groups Definition

A functional group or moiety is a specific group of atoms within a molecule that is responsible for characteristic chemical reactions of that molecule. No matter what size a molecule is, a functional group participates in chemical reactions in a predictable manner.

Functional groups link to the rest of the molecule via covalent bonds. The group may be neutral or charged.

Functional Group Examples:

Examples of common functional groups include alcohol (-OH), aldehyde (-COH), and nitrile (-CN).


The naming convention for moieties describes whether it is saturated or unsaturated and whether it contains single, double, or triple bonds.

Class Formula Suffix Example
Single bond R• -yl Methyl group, Methyl radical
Double bond R: -ylidene Methylidene
Triple bond R⫶ -ylidyne Methylidyne
Carboxylic acyl radical R−C(=O)• -oyl Acetyl


  • Brown, Theodore (2002). Chemistry : The Central Science. Upper Saddle River, NJ: Prentice Hall. p. 1001. ISBN 0130669970.
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Helmenstine, Anne Marie, Ph.D. "Functional Groups Definition and Examples." ThoughtCo, Aug. 26, 2020, Helmenstine, Anne Marie, Ph.D. (2020, August 26). Functional Groups Definition and Examples. Retrieved from Helmenstine, Anne Marie, Ph.D. "Functional Groups Definition and Examples." ThoughtCo. (accessed March 23, 2023).