MNDO/GIAO PERTURBATION THEORY OF NMR SHIELDING CONSTANTS

By virtue of gauge-invariant atomic orbitals (GIAO), the basic approximations of MNDO method have been applied to the SCFMO theory of nuclear magnetic shielding constants. The derived equations are used to calculate NMR shielding constants. A simpler and more effective integration for 1-electron operators 1/ r m , L m , and L m / r m is proposed. By proper selection of MNDO parameters and the 2-center approximation, a satisfactory agreement is obtained between the calculated and experimental 13 C shielding constants for a representative set of hydrocarbons.