Quantum chemical bond order as a local descriptor for modelling reaction paths

Abstract

The feasibility of studying chemical reactions by focusing attention only on the bonds actively involved in the reaction process is explored. Active bond order (BO) profiles are shown frequently to be characterized by the occurrence of sharp inflexions at a point close to the saddle point on the reaction path. The sum of the active BOs is shown to remain approximately conserved. Active BOs may therefore be used as a local descriptor of the reaction path. This leads to extended bond-energy bond-order (EBEBO) postulates which are proposed to transcribe an essentially local picture of a reaction as a superposition of elementary chemical events into a semi-global description. A local Hammond postulate and its ramifications are explored along with a local measure of the asynchronicity of the bond-breaking and bond-making processes in a chemical reaction. The origin of BO inflexions is theoretically sought to be connected with Fermi correlation.