functional group

https://doi.org/10.1351/goldbook.F02555
Organic compounds are thought of as consisting of a relatively @U06567@ @B00574@, for example a chain of \(\text{sp}^{3}\) hybridized carbon atoms, and one or several functional groups. The functional group is an atom, or a group of atoms that has similar chemical properties whenever it occurs in different compounds. It defines the characteristic physical and chemical properties of families of organic compounds.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1116 [Terms] [Paper]