Ab initio calculations have been carried out to investigate bonding patterns and B−N coupling constants in five-membered rings N3B2H4X and N2B3H4X, for X = H, F, and Li, with substitution occurring only at N. F-substitution results in the formation of a covalent N−F bond, whereas Li-substitution leads to an ion-pair with little covalency. Substitution has a highly localized effect, changing the electron density only at the substituted N. F-substitution also has a very localized effect on coupling constants, at most only changing 1J(B−N) involving the substituted N. Li-substitution has a more delocalized effect. It always decreases 1J(B−N) involving the substituted N, and may also decrease 1J(B−N) of a proximal B−N bond if the B atom is bonded to the substituted N
