VICINAL PROTON PROTON COUPLING-CONSTANTS - BASIS SET DEPENDENCE IN SCF ABINITIO CALCULATIONS

An SCF ab initio study of the angular dependence and substituent effec ts upon the vicinal coupling constants has been carried out for the mo lecules CH3CH3, CH2FCH3 and CHF2CH3. The four contributions to 3J(HH) (J(FC), J(SD), J(OD) and J(OP)) have been computed using the STO-3G, 6 -31G, 6-31G and 6-31G** basis sets. The major contributions arise fro m the FC term. The magnitude of the SD contributions is very small and near independent of the size of the basis set. The magnitude of the o rbital contributions OR (=OD+OP) decreases as the size of the basis se t increases. The FC term slightly overestimates both the individual an d the interaction substituent effects for basis sets larger than the S TO-3G one. For this basis such effects are underestimated.