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.