Nucleophilic addition to a carbonyl is the addition of a nucleophile to the electron-deficient carbon of a carbon–oxygen double bond (C=O). It matters as the characteristic reaction of aldehydes and ketones. Unlike the carboxylic acid derivatives, an aldehyde or ketone has no leaving group on the carbonyl carbon, so the tetrahedral species that forms cannot expel a group; the result is therefore addition rather than the substitution seen with acid derivatives.

对羰基的亲核加成是亲核试剂加到碳氧双键(C=O)缺电子碳上的反应。它之所以重要,是因为它是醛和酮的特征反应。与羧酸衍生物不同,醛或酮的羰基碳上没有离去基团,因此所形成的四面体物种无法排出基团;故结果是加成,而不是酸衍生物所见的取代。