S. C. Choi

A bond-length-bond-order relationship for intermolecular interactions based on the topological properties of molecular charge distributions.

Abstract Ab initio SCF MO calculations for the hydrogen-bonded complexes between nitriles and hydrogen fluoride suggest a strong linear relationship between the charge density at the hydrogen-bond critical point and the hydrogen-bond energy. Further investigation of the topological properties of the charge density indicates that the generalization of the bond-length-bond-order relationship of CC bonds due to Bader et al. may be extended to intermolecular hydrogen bonding. Calculations at the 6–31G ** level, including complete geometry optimization, are reported for the complexes, where R  H, Li, F, Cl, HO, LiO, NC, HCC, CH 3 and CH 3 O.

Hydrogen bonding between nitriles and hydrogen halides and the topological properties of molecular charge distributions

Abstract The topological properties of the charge density of the hydrogen-bonded complexes between nitrites and hydrogen chloride correlate linearly with theoretical estimates of the hydrogen-bond energy. At the 6-31G** level, the hydrogenbond energies range from a low of 10 kJ mol m NCCN—HC1 to a high of 38 kJ mol in LiCN—HCl. A linear relationship between the charge density at the hydrogen-bond critical point and the NH internuclear distance of the RCN—HC1 complexes indicates that the generalization of the bond-length-bond-order relationship of CC bonds due to Bader, Tang, Tal and Biegler-Konig can be extended to intermolecular hydrogen bonding.

Electronic and structural properties of borazine and related molecules

Abstract Ab initio SCF MO calculations are reported for benzene, s -triazine, borazine and boroxine. The Laplacian of the charge density and the Mulliken population analysis procedure demonstrate that the delocalization of the π electrons decreases and the polarity of the ring bonds increases substantially as the atoms in the ring become more dissimilar. Several other properties, including distortion of the ring angles, puckering of the ring and nuclear quadrupolar coupling constants, emphasize the different chemical properties within the isoelectronic series.

Bond length and the electron density at the bond critical point: X--X, Z--Z, and C--Z bonds (X = Li-F, Z = Na-Cl).

The aim was to investigate the relationship between the bond length and the electron density at the bond critical point in homonuclear XX and ZZ and heteronuclear CZ bonds (X = Li‐F, Z = Na‐Cl). The d,ρc pairs were obtained from 472 target bonds in DFT‐optimized (B3LYP/6‐311+G(d,p)) small molecular species. These species were selected arbitrarily but with a view to maximize the range widths WR for each atom combination. It was found that (i) with one clear exception, the d(A − A) means (A = X or Z) correlate linearly with the bond lengths d(A2) of the respective diatomic molecules; (ii) the d(A − A) means correlate parabolically with n, the formal number of valence electrons in the atoms of the bond; and (iii) with increasing sample size N the ratio WR(ρc)/WR(d) appears to converge toward a representation f [WR(ρc)/WR(d)]N→∞ characteristic of A. Detailed analysis of the d,ρc relationship has shown that by and large simple power regression accounts best for the DFT data. The regression coefficients of d = aρ  c−b and ρc = αd−β (b, β > 0) vary with n in a seemingly irregular manner but one that is consistent with simple chemical notions. The d(A2) can be approximated in terms of multilinear MO electron occupancies.