Ordinarily the nitrogen atom in the amine group is reacting as a nucleophile by way of its lone pair. This polarity can be reversed when a primary or secondary amine is substituted with a good leaving group (such as a halogen atom or an alkoxy group). The resulting N-substituted compound can behave as an electrophile at the nitrogen atom and react with a nucleophile as for example in the electrophilic amination of carbanions.