Effect of the heavy atom on the nuclear shielding constant. I. The proton chemical shifts in hydrogen halides

Abstract

The abnormal upfield bias of the proton chemical shift in hydrogen halides, HX, on going from X = F to I is examined theoretically in terms of the third-order perturbation theory including the spin-orbit interaction (λL · S). The expression for the new type of shielding constant σLS is presented in its complete form and in simplified form with the average excitation energy approximation. The numerical calculations using semiempirical SCF wavefunctions predict substantial contribution (51%) of this shielding effect (σLS) to the total shielding of the proton in hydrogen iodide.