GIAO Calculations of Chemical Shifts of NMR Spectra of H-1 and C-13 of the Hexahydroindoles Products

Isotropic H-1 and C-13 nuclear magnetic shielding constants of hexahydroindoles products of intramolecular Diels-Alder of the triene-amide reaction have been calculated by employing the gauge-including-atomic-orbital (GIAO), Continuous Set of Gauge Transformations (CSGT) and a slight variation on the CSGT (IGAIM) methods at the B3LYP/6-311(d,p) density functional level of theory. Geometry of each compound has been optimized employing 6-31G(d,p) basis sets. The comparison of the theoretical results to the experimental results of the Ha compound shows that the GIAO method is the most reliable. On the other hand we calculate the chemicals shifts of the carbon (C-13) and hydrogen (H-1) of the Hb and Hc compounds. This calculation was performed using the B3LYP functional, using the GIAO method at the level of the following bases: 6-31G, 6-31 G(d), 6-31G(d, p), 6-311G, 6-311G(d). The theoretical trends are compared with experimental data taken from the literature. The least squares regression analyses of the results indicate R-square values greater than 0.90 in the range for total data set.