THEORETICAL STUDY OF THE CHALCOGEN-CARBON COUPLING CONSTANTS IN THE CHALCOGEN HETEROCYCLOPENTADIENES

Abstract The three contributions (Fermi-contact, orbital-dipole, and spin-dipole) to the chalcogen-carbon coupling constants of selenophene, tellurophene and a number of their derivatives have been examined by SCF-INDO perturbation theory calculations. All three types of spin-spin interaction are important and, in particular, the direct coupling is controlled by the orbital-dipole and Fermi-contact terms. Correlative arguments and theoretical calculations have been used to predict the sign and order of magnitude of the n J( 33 S 17 O  1 H 13 C ) coupling contants of the congener systems thiophene and furan.