AB-INITIO AND EXPERIMENTAL-STUDY OF NMR COUPLING-CONSTANTS IN BICYCLO[1.1.1]PENTANE

The different dependences of NMR spin-spin coupling constants of a med ium-sized molecule on the quality of the ground-state wavefunction is studied using three different basis sets of increasing size, namely, 6 -31G, 6-31G and 6-31G**. Calculations of the Fermi contact terms were also carried out using partially uncontracted s and p atomic orbitals with the same exponents as those of the 6-31G basis set. Bicyclo[1.1. 1]pentane was chosen as a model compound; it was synthesized for the m easurement of several couplings as part of this work in order to compa re theoretical results with experimental values. The through-space tra nsmission of couplings via the interaction of rear lobes of orbitals i nside the bicyclic cage were studied with the IPPP approach using the above basis sets.