The zwitterion of N-(2-carboxyphenyl)-4-dimethylaminebenzylideneimine

The crystal and molecular structures of N-(2-carboxyphenyl)-4-dimethylaminebenzylideneimine and its protonated form have been determined. The Schiff base exists as the zwitterion, which is stabilized by the intramolecular ionic hydrogen bond. According to quantum-mechanical calculation results this tautomeric form is energetically unfavorable but in the solid and liquid state the intermolecular interactions support zwitterionic form.