The use of bond paths for quantitatively characterizing bond strain

The concept of the bond path as a means for characterizing individual strained bonds is developed in detail and applied to a variety of molecules. A reference path is defined in terms of the superposed electronic densities of the free atoms, and a “bond deviation index” is introduced, for expressing quantitatively the difference between the actual and the reference bond paths. This difference is taken as indicating the degree of strain in the bond. It is shown that bond paths can be significantly affected by not only neighboring bonding electrons, but by lone pairs as well, as in the H₂O and NH₃ molecules.