Analyze chemical bonding with Chemissian

Chemissian offers "Analyze bonds" tool to analyze bonding inside a molecule - in one table interatomic distance, overlap populations and bond orders are presented for every bond.

In the figure above such analysis is performed for ethylene molecule. As can be seen bond order for C-C bond is very close to 2 ("double bond"), as it should be from the classical viewpoint. It is to be noted that Chemissian can also calculate bond orders for generalized bond - bond between molecular fragments.

About bond orders:
When performing quantum-chemical calculation it is very important to analyze electronic structure of molecules in terms of "classical conceptions". Bond order is one of such conception: classically it is defined as the number of chemical bonds between a pair of atoms or as the difference, divided by two, between the number of bonding molecular orbitals and the number of antibonding MOs (in diatomic homonuclear molecules with closed shells).

In the 1960-1980th this conception was extended to the case of any molecule (not only diatomic) and it was introduced quantum-chemical bond order by Wiberg, Giambiagi, Borisova, Semenov and Mayer. These bond orders are in accordance with classical structural chemistry conceptions, e.g. quantum chemical bond order index for C-C bond in ethane gives value close to 1.0 (single bond), in ethylene BO is close to 2 (see figure above), for acetylene BO is about 3 (triple bond), in benzene it is close to 1.5, etc. Bond order characterizes covalent bonding between atoms in molecule.

The concept of quantum-chemical bond orders is closely connected with the conception of valence indexes.