Markovnikov's rule is an empirical rule stating that, in the electrophilic addition of a hydrogen halide (H–X) to an alkene, the hydrogen adds to the carbon of the double bond that already bears more hydrogens (the less-substituted carbon). It matters because it predicts the major product of such additions. The underlying reason is that this mode of addition generates the more stable carbenium ion, which forms more readily and so determines the regioselectivity.

马尔科夫尼科夫规则(马氏规则)是一条经验规则,指出在卤化氢(H–X)对烯烃的亲电加成中,氢加到双键上原本含氢较多的那个碳(取代较少的碳)上。它之所以重要,是因为它能预测这类加成的主产物。其根本原因在于,这种加成方式生成较稳定的碳正离子,后者更易形成,从而决定区域选择性。