官能团（英文：Functional group），是决定有机化合物的化学性质的原子和原子团。

根据所含π键的不同，不同的烃基官能团具有不同的性质。注意：烷烃基（如甲基、亚甲基）不算官能基，而苯基是官能基。

卤代烃中含有碳-卤素键，键能随卤素不同而有变化。一般除氟代烃外，卤代烃都可发生亲核取代反应和消去反应。

不同的碳氧键会因其中原子杂化程度的不同而有性质上的差异。sp杂化的氧原子有吸电子效应，而sp则有给电子效应。

alkyl nitrate

alkanenitrile
alkyl cyanide

alkyl nitrite

In organic chemistry, functional groups are specific groups (moieties) of atoms or bonds within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction(s) regardless of the size of the molecule it is a part of. However, its relative reactivity can be modified by other functional groups nearby. The atoms of functional groups are linked to each other and to the rest of the molecule by covalent bonds. When the group of covalently bound atoms bears a net charge, the group is referred to more properly as a polyatomic ion or a complex ion. Any subgroup of atoms of a compound also may be called a radical, and if a covalent bond is broken homolytically, the resulting fragment radicals are referred as free radicals.