Moiety Definition in Chemistry

Kekulene molecular structure

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In chemistry, a moiety is a specific group of atoms within a molecule that is responsible for characteristic chemical reactions of that molecule. Although sometimes the terms moiety and functional group are interchanged, a functional group is a smaller group of atoms. Moieties are branches in organic molecules that extend from the carbon backbone. Often, moieties may be substituted with other substituents or side chains.

In pharmacology, an active moiety is the portion of an ion or molecule responsible for the activity of a drug.

Examples: hydroxyl moiety: -OH
aldehyde moiety: -COH