Calculation of ¹³C‐NMR chemical shift using the intermediate neglect of differential overlap model

Abstract

The local origin/local orbital (LORG) method of Hansen and Bouman has been implemented with the intermediate neglect of differential overlap Hamiltonian for spectroscopy (INDO/S). The method is shown capable of demonstrating the inductive effects associated with electronwithdrawing substituents through the diamagnetic shielding term. In addition, the method is capable of differentiating chemical shift in differing bond environments. The calculated paramagnetic contribution, however, is deficient for substituents that saturate the minimal basis such as oxygen and fluorine, which severely limits the general utility of the procedure. Through the utilization of reduced linear equations for the paramagnetic term, the method is amenable to any molecule for which a self-consistent field can be performed and therefore can potentially be used to study very large systems. At present, however, the LORG method when used with the rapid INDO/S model Hamiltonian does not reliably reproduce the paramagnetic contribution to the shielding.

13C NMR Chemical Shift Calculations for Some Substituted Pyridines: A Comparative Consideration

“…(C) Semiempirical Calculations. The HyperNMR program from Hypercube − uses the TNDO (typed neglect of differential overlap) method (version 1 and version 2) for quantum-chemically computing the various chemical shifts ( 13 C included). The semiempirical parameters for the TNDO/1 and TNDO/2 quantum mechanical approach were reparametrized by the authors in order to give more acceptable chemical shifts and also coupling constants.…”

NMR chemical shifts in MNDO approximation: Parameters and results for H, C, N, and O

“…two special-purpose sum-over-states SOS MNDO implementations, 53,54 gauge-dependent LORGINDOr S, 55 and the commercial TNDOr2 method. 56,57 Only FPT-MNDOrGIAO and TNDOr 2 have been designed as general purpose methods and therefore merit some comments in the present context.…”