Density functional calculations exploring the methylene-water interaction in the gas phase and in solution

Results are presented from density functional calculations which investigate the interaction between water and singlet methylene. Geometries, energies, and vibrational frequencies were characterized for a number of local minima and transition states on the water-methylene potential energy surface in the gas phase and in solution. The solution phase studies were carried out using the Onsager reaction field model with a range of dielectric constants from 2 to 80. Calculations were performed using density functional theory with the B3LYP functional. The 6-31G* and 6-311++G** basis sets were employed for all calculations. When results are compared to MP2 and QCISD studies, it is found that density functional theory overestimates the binding energies of the ylides formed between methylene and water. In addition, density functional theory poorly describes the energetics of the ylide rearrangement via a 1,2-hydrogen shift mechanism to form methanol. The barrier for rearrangement is underestimated by density functional theory when compared to MP2 or QCISD results. However, density functional theory qualitatively predicts the stabilization of the methylene-water ylides and the increase in barrier height for rearrangement in solution. (C) 1998 Elsevier Science B.V.