Ab initio conformational analysis of α-aminoaldehydes and α-aminoketones in the gas phase and in aqueous solution

The ab initio conformational analysis of 10 alpha-aminoaldehydes and alpha-aminoketones containing the N-C-C=O moiety was carried out at the HF/3-21G, HF/6-31G** and MP2/6-31G** levels. Conformational preferences are mainly interpreted in terms of different kinds of intramolecular hydrogen bonding, although other effects should also be considered. These effects explains the energetic and geometrical differences observed between N-C-C=O and related C-C-C=O compounds. Finally, by means of an ab initio method for the treatment of the solvent as a continuum (polarizable continuum model, PCM), the influence of water on the conformational stabilities was estimated. Significant changes in relative energies were found, which were related to the interaction between the dipole moment of the solute and the reaction field of the solvent, although local dipolar interactions or the presence of hydrogen bonding in certain conformations can also be important. (C) 1998 Elsevier Science B.V. All rights reserved.