Ab Initio NMR Study of the Isomeric Hydrogen-Bonded Methanol–Water Complexes

Isotropic and anisotropic chemical shifts for all atoms of complexes CH3HO . . . H2O and CH3OH . . . OH2 have been calculated at the Hartree–Fock, secondorder Møller-Plesset (MP2) and density functional (B3LYP) theoretical levels using the 6-311 G(2d,2p) basis set. The influence of the hydrogen bond formation on the nuclear magnetic resonance chemical shifts in all atoms is analyzed. The basis set superposition error was taken into account, and its effects were more significant for the anisotropic shieldings on the oxygen atoms of the proton donor CH3OH . . . OH2 and proton acceptor methanol CH3HO . . . H2O. Using counterpoise correction to the MP2 results, our best estimate for the calculated isotropic and anisotropic shifts of the H atom involved in the hydrogen bond are 2.98 and 11.95 ppm for CH3HO . . . H2O and 2.91 and 11.48 ppm for the CH3OH . . . OH2 isomer, respectively. For the O atom of the OH hydrogen bonded, these calculated shifts are 5.21 and 5.35 ppm for CH3HO . . . H2O and 6.32 and 8.75 ppm for CH3OH . . . OH2. The effect of monomer relaxation was also considered and was found to be appreciable only for the oxygen atom of the proton donor OH due to the distance increase after complex formation. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem 102: 554–564, 2005