Strength of the NH···OC and CH···OC Bonds in Formamide andN-Methylacetamide Dimers

作者：Rubicelia Vargas, Jorge Garza, Richard A. Friesner, Harry A. Stern, Benjamin P. Hay, David A. Dixon · 发表于：The Journal of Physical Chemistry A · 年份：2001 · DOI：10.1021/jp003888m · 被引用次数：157 · 研究领域：Advanced Chemical Physics Studies、Crystallography and molecular interactions、Nonlinear Optical Materials Research

The structures of the dimers of formamide and N -methylacetamide have been calculated at the ab initio electronic structure theory level, second-order Møller−Plesset perturbation theory (MP2) with augmented correlation consistent basis sets. Five unique structures were optimized for the formamide dimers at the MP2/aug-cc-pVDZ and MP2/aug-cc-pVTZ levels. At the optimized geometries obtained with the aug-cc-pVTZ basis set, MP2 energies were evaluated with the aug-cc-pVQZ basis set, allowing an extrapolation of the energies to the complete basis set limit. Four structures were found for the N -methylacetamide dimer at the MP2/aug-cc-pVDZ level, and single-point energies were calculated at the MP2/aug-cc-pVTZ level. In both systems, the basis set superposition error was estimated with the counterpoise method. The strength of the N H···O C bond has a mean value of 7.1 kcal/mol in the formamide dimers and a mean value of 8.6 kcal/mol in the N -methylacetamide dimers. The difference in hydrogen bond strengths is attributed to differences in basicity at the carbonyl oxygen receptor site. In several dimers C H···O C hydrogen bonds play an important role in stabilizing these intermolecular complexes, increasing the interaction energy by 1.1−2.6 kcal/mol per interaction.