Monte Carlo and molecular orbital study of solvent effect on the electronic structure and hyperfine coupling constants of the (CH3)2NO radical: the effect of electron transfer between the solute and solvent molecules Original Research Article

Ab initio UHF MIDI-4 calculations have been carried out for the dimethyl nitric oxide (DMNO) radical in the H2O and CHCl3 solutions. The configurations of the solvent molecules were selected from the snapshots in the Monte Carlo (MC) simulation for the solution, and the electronic structure and the hyperfine coupling constant (hfcc) of DMNO were obtained by averaging the results of 300 configurations. The point charge approximation in which all solvent molecules were represented by point charges indicated that the electrostatic interaction polarizes the N–O bond and increases the spin density on the N atom. When some of the solvent molecules near DMNO were treated as a supermolecule together with DMNO and the remaining solvent molecules were approximated by point charges, the electron transfer occurs between DMNO and H2O molecules in two directions, from DMNO to H2O around the N–O group and from H2O to DMNO around the CH3 groups. These electron transfers polarize the N–O bond in the same direction as the electrostatic interaction and increase the hfcc of the N atom. The contribution of the electron transfer accounts for 40% of the solvent effect on hfcc of DMNO.