An alkyl halide, also called a haloalkane, is an organic compound in which one or more hydrogen atoms of an alkane are replaced by halogen atoms, giving carbon–halogen (C–X) bonds. It matters because the polar C–X bond makes the carbon electrophilic, so alkyl halides readily undergo nucleophilic substitution and elimination and serve as versatile starting materials. The halogen here is the functional group, in contrast to the unreactive C–H bonds of the parent alkane.

卤代烷,又称卤代烃,是烷烃中一个或多个氢原子被卤素原子取代、从而形成碳–卤(C–X)键的有机化合物。它之所以重要,是因为极性的 C–X 键使碳带亲电性,故卤代烷易发生亲核取代和消除反应,并可作为用途广泛的起始原料。此处卤素即为官能团,与母体烷烃中不活泼的 C–H 键形成对照。