Intramolecular Hydrogen Bonding, Gauche Interactions, and Thermodynamic Functions of 1,2-Ethanediamine, 1,2-Ethanediol, and 2-Aminoethanol: A Global Conformational Analysis

The global conformational potentials of 1,2-ethanediol, 1,2-ethanediamine, and 2-aminoethanol (X−CH2−CH2−Y; X, Y = OH or NH2) were obtained at the MP2/6-311+G(2d,p) level by scanning through the dihedral angles of the two functional groups and the carbon−carbon bond with the remaining nuclear coordinates being energy-minimized. It was found that the potentials could be represented by the direct-bond potentials between the adjacent molecular fragments and by the through-space electrostatic potentials between the vicinal and geminal fragments. Here, the through-direct-bond potentials are represented by the conventional three Fourier terms of the internal rotation angles, and the through-space potentials, which include the intramolecular hydrogen bonding between X and Y, are represented by the general functional forms of the electric dipole−dipole, dipole−quadrupole, and quadrupole−quadrupole interaction terms. The fitted electrostatic interaction strengths between the X and Y fragments are in good agreement...