CNDO/2 calculations and configuration analyses for some hydrogen-bonded systems

Abstract

The potential energy curves of hydrogen-bonded systems were calculated for the water, methanol, and formic acid dimers and for the hydrogen maleate ion by a modified CNDO/2 method, the core resonance integrals betweenσ-electrons being distinguished from those betweenπ-electrons, the different bonding parameters being used for -O- and =O, and the core potential integralsV AB c for O-H, C=O, and O...O being determined semi-empirically. Consequently, the following results were obtained: 1) a potential energy curve with a single minimum atr(O-H)=0.95 A and with a concavity near 1.70 A for the linear chain dimers of water and methanol; 2) a symmetrical potential energy curve with two minima atr(O-H)=0.95 and 1.78 A for the cyclic dimer of formic acid; 3) a flat-bottomed symmetrical potential energy curve for the hydrogen maleate ion. The configuration analysis method was applied to the hydrogen-bonded systems; the contributions of the covalent ((O-H-O)−1) and ionic (O−H+O−) structures being 54% and 39%, respectively, for the symmetrical hydrogen bonding of the hydrogen maleate ion.