VALENCE BOND ALTERNATIVES TO DOUBLE-BONDS AND TRIPLE BONDS

The results of ab initio valence bond calculations for dinitrogen show that resonance between the valence bond structures [GRAPHICS] with electron-pair sigma-bonds and one-electron pi-bonds, generates a lower energy than does the triple-bond structure [GRAPHICS] with Coulson-Fischer-type wavefunctions for the two pi-bonds. When the wavefunctions for these two sets of structures are expressed as linear combinations of wavefunctions for nine canonical Lewis structures, it is found that the triple-bond structure overestimates the importance of the high polar canonical structures [GRAPHICS] and this is the origin of the higher energy for the triple-bond structure.