Two photoisomerization mechanisms of 4-amino-3-penten-2-one: Hydrogen-atom migration and internal rotation

A non-chelated keto-enamine isomer is produced from a chelated 4-amino-3-penten-2-one upon UV irradiation by internal rotation around the CHC bond with braking the intramolecular hydrogen bond, while an imino-enol isomer is produced by hydrogen-atom migration from the amino group to the carbonyl group with retaining the intramolecular hydrogen bond.