Molecular Electrostatics for Exploring Complexes of Carbonyl Compounds and Hydrogen Fluoride

The negative-valued molecular electrostatic potential (MESP) minima ( V min ) observed in the substituted carbonyl molecules are found to be a sensitive measure for the analysis of the electronic charge perturbations due to the substituents. MESP topography of eight monosubstituted aliphatic carbonyl molecules (HCOR: R = H, F, Cl, CN, OH, SH, NH 2, CH 3, CF 3, NO 2 ) [following Bobadova-Parvanova, P.; Galabov, B. J. Phys. Chem. A 1998, 102, 1815] is carried out at the HF-SCF/6-31G** level for assessing this scheme. The V min values are seen to clearly reflect the changes due to the electron donating/withdrawing substituents. The electrostatic potential for intermolecular complexation (EPIC) model is used for predicting the possible hydrogen-bonded structures of the carbonyl molecules with the hydrogen fluoride. These complexes are further optimized at the HF-SCF/6-31G** level of theory. An excellent linear correlation is obtained with EPIC energy and the corresponding optimized interaction energy of the complex. Total correction to the ab initio SCF interaction energy due to basis set superposition error and zero-point energy is found to be about 40% of the SCF interaction energy. The HF molecule binds from the nonsubstituted sides of the HCOR molecules for R H, F, Cl, CN, and CF 3 . On the other hand, it is seen to bind from the substituted side for R OH, SH, NH 2, and CH 3 . The effect of substitution on the charge distribution and on hydrogen bonding is discussed.