GIAO-SCF CALCULATION OF THE CHEMICAL-SHIFTS IN SIMPLE ENAMINES - A COMPARISON OF THEORY WITH EXPERIMENT

Methyl-substituted enamines assume overwhelmingly a gauche-out conform ation in the absence of steric hinderance. A change of global minimum to the orthogonal-out structure occurs in the presence of steric inter actions (Z-substitution pattern), Calculation of the C-13 NMR shift at the beta-carbon atom as a function of the torsional angle about the C -N bond axis reveals that the experimentally observed differential shi elding is directly dependent upon the conformation asssumed by the ena mine. The GIAO-SCF method reproduces the observed shift difference at C-beta quite satisfactorily. Furthermore, we show that, at least in th e case of methyl-substituted enamines, conformational assignments in s olution can be made upon comparison of theoretical with experimental C -13 NMR spectra.