These pages are best viewed with a width of 7 inches.
Glaser et al. (ref. to J. Am. Chem. Soc. 1991, 113, 1109.) resisted the temptation to pull an explanation from the conventional menu and append it to their calculations. Rather they came to the conclusion that "the structural and topological features of the CN linkages in MeN2+ and EtN2+ are similar and their consideration alone cannot account for the large difference in their dissociation energies. ... The characterization of the electron density in the bonding region alone is not sufficient to fully characterize all of the bonding properties." This is precisely the spirit of the T formula: Stability is the result of what happens interactively in the entire molecule (how all bonds arrange themselves so as to minimize mutual exchange repulsion) rather than what happens at an isolated bond or subfragment.