Conformational and Tautomeric Preferences in 3-Aminoacrylaldehyde: A Theoretical Study

The conformational study of 3-aminoacrylaldehyde were performed at various theoretical levels and the equilibrium conformations were determined. Furthermore, to have more reliable energies, the total energies of all forms recomputed at G2MP2 and CBS-QB3. Theoretical calculations clearly show that the intramolecular hydrogen bond (IHB) is the origin of conformational preference and the resultant IHB order at HF/6-311++G(d,p), MP2/6-311++G(d,p), and CBS-QB3 levels is different from the order which obtained from the B3LYP/6-311++G(d,p), G2MP2, the geometrical parameters, AIM, and NBO analyses. Furthermore, our theoretical results reveal that the ketoamine (KA) tautomeric group is more stable than the enolimine (EI) and ketoimine (KI) ones. The IHB and tautomeric process could not rationalize the irregular stability of KA group with respect the others. But the population analyses of the possible conformations by NBO predict that the pi-electron delocalization, especially unusual pi(*)(C = C) -> pi(*)(C = O) charge transfer, is the origin of tautomeric preference. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 111: 586-595, 2011