Computation of 3 J HH coupling constants with a combination of density functional theory and semiempirical calculations. Application to complex molecules.

Abstract: This work evaluates the efficiency of economic levels of theory for the prediction of ³ J _HH spin–spin coupling constants, to be used when robust electronic structure methods are prohibitive. To that purpose, DFT methods like mPW1PW91, B3LYP and PBEPBE were used to obtain coupling constants for a test set whose coupling constants are well known. Satisfactory results were obtained in most of cases, with the mPW1PW91/6-31G(d,p)//B3LYP/6-31G(d,p) leading the set. In a second step, B3LYP was replaced by the semiempirical methods PM6 and RM1 in the geometry optimizations. Coupling constants calculated with these latter structures were at least as good as the ones obtained by pure DFT methods. This is a promising result, because some of the main objectives of computational chemistry – low computational cost and time, allied to high performance and precision – were attained together. [Copyright &y& Elsevier]