On the correlation of bond order and bond length

Abstract

The correlation between bond orders calculated from ab initio wave functions and bond length is investigated. Bond orders were obtained using Mayer's definition (Int. J. Quantum Chem. 29 (1986) 73, 477) at the transition structures and geometries along the minimum energy paths for a number of chemical reactions. The bond orders decrease exponentially with the increase of the bond length, R. We found that the formula Pauling proposed to define “chemist's bond order”, n=exp[−(R−R0)/b] (where R0 is the equilibrium bond length of a single bond) describes the correlation well. By fitting his equation to the data, the parameter b was found to be 0.373±0.011, 0.378±0.015 and 0.256±0.025Å, for C–C, C–O, and C–H bonds, respectively. The goodness of the correlation supports the idea of using this formula when a bond order–bond length correlation is needed, like in the bond energy–bond order method.