Analysis of bonding properties in molecular ground and excited states by a Cohen‐type bond order

We propose a Cohen‐type bond order analysis in terms of orthogonalized atomic basis functions which can be used to analyze NDO wave functions of large organic and metal–organic molecules. It is shown that for small molecules the results gained with this method are in excellent agreement with the same analysis based on ab initio STO ‐3G wavefunctions. For large planar aromatic systems these all‐valence electron bond orders are found to be a consistent generalization of the π‐bond order. A simple relation between these bond orders and the corresponding covalent bond energies is established. The method can be easily extended to study excited state multiconfiguration wave functions. We present calculations for C 2 H 2 , C 2 H 4 , C 2 H 6 , and Mn 2 (CO) 10 . The results indicate that the method can be used to discuss the photochemistry of organic and metal–organic compounds.