Analysis of isotope effects in NMR one-bond indirect nuclear spin-spin coupling constants in terms of localized molecular orbitals

Abstract

We recently showed, by analyzing contributions from localized molecular orbitals, that the anomalous deuterium isotope effect in the one-bond indirect nuclear spin–spin coupling constant of methane, also called the unexpected differential sensitivity, can be explained by the transfer of s-orbital character from the stretched bond to the other unchanged bonds [ChemPhysChem, 2008, 9, 1259]. We now extend this analysis of isotope effects to the molecules BH4−, NH4+, SiH4, H2O and NH3 in order to test our conclusions on a wider rage of XH4 compounds and to investigate whether the lone-pair orbitals are really responsible for the absence of a similar effect in water and ammonia as proposed earlier [J. Chem. Phys., 2000, 113, 3121].