Secondary amines add to aldehydes and ketones to give enamines. Enamines are formed in a reversible, acid-catalyzed process that begins with nucleophilic addition of the secondary amine to the carbonyl group, followed by transfer of the proton to yield a neutral carbinolamine. Protonation of the hydroxyl group converts it into a good leaving group, however there is no hydrogen left on the nitrogen to be lost to form a neutral imine product. Instead, a proton is lost from the neighboring carbon to form an enamine. Draw curved arrows to show the movement of electrons in this step of the mechanism.