Density functional and Møller-Plesset studies of cyclobutanone[...]HF and [...]HCl complexes.

The molecular structure (hydrogen bonding, bond distances and angles), dipole moment and vibrational spectroscopic data [vibrational frequencies, IR and vibrational circular dichroism (VCD)] of cyclobutanonecdots, three dots, centeredHX (X = F, Cl) complexes were calculated using density functional theory (DFT) and second order Møller-Plesset perturbation theory (MP2) with basis sets ranging from 6-311G, 6-311G(**), 6-311 + + G(**). The theoretical results are discussed mainly in terms of comparisons with available experimental data. For geometric data, good agreement between theory and experiment is obtained for the MP2 and B3LYP levels with basis sets including diffuse functions. Surface potential energy calculations were carried out with scanning HCl and HF near the oxygen atom. The nonlinear hydrogen bonds of 1.81 A and 175 degrees for HCl and 1.71 A and 161 degrees for HF were calculated. In these complexes the C=O and H-X bonds participating in the hydrogen bond are elongated, while others bonds are compressed. The calculated vibrational spectra were interpreted and the band assignments reported are in excellent agreement with experimental IR spectra. The C=O stretching vibrational frequencies of the complexes show red shifts with respect to cyclobutanone.