Description of covalent bond orders using the charge density topology

Hybrid density functional calculations are employed to explore the relationships between covalent bond order, as defined using the atomic overlap matrix (AOM) formalisms developed by Cioslowski, Angyan and others, and the parameters derived from a topological analysis of the electron density. Relationships are obtained for the specific cases of C—C, C—N, C—O, C—P and C—S bonds. The simple Pauling bond order–bond length relationship describes the data reasonably well in most cases, but the correlations show considerable scatter. Although no single parameter acts as a unified descriptor of bond order for all types of bond, in each case it is possible to find a model which describes the bond order data significantly better than the Pauling model based on bond length. The relationships presented can therefore be utilized to estimate rapidly the covalent part of the bond order from a topological analysis of the charge distribution for very large systems where the AOM-based methods can become impractical to apply, and for charge density distributions which have been obtained from experiment (e.g. elastic x-ray scattering). Copyright © 2003 John Wiley & Sons, Ltd.