Ab initio investigations of hydrogen bonding in aliphatic N-oxide–water systems

Abstract

Aliphatic N-oxide–water mixtures play an important role as solvents in industrial cellulose processing. Yet it is unknown why certain compounds dissolve cellulose and others do not. In order to understand the microscopic reasons for these differences extensive ab initio Hartree–Fock and post-Hartree–Fock calculations were carried out for different aliphatic N-oxides and their monohydrates. Optimal geometries, charges, and dipole moments were calculated with the 6-31G** basis set. Atomic point charges were calculated based upon Mulliken population analysis and as `electrostatic potential derived' (ESP) charges. H-bond energies were determined with the 6-311+G(2 d,2 p) basis set. Resulting from the high dipole moments of the N–O bonds, large H-bond energies were found. As expected, the ESP charges represent the dipole moment resulting from the wavefunction better than the Mulliken charges. The dipole moments of the hydrated N-oxides and of the hydrated N–O bonds are less than those of the unhydrated species.