ELECTRIC-FIELD EFFECTS ON THE C-13 AND F-19 NUCLEAR SHIELDING IN HF AND CH3F

In a uniform electric field changes take place in some or all of the tensor components of nuclear shielding. For small fields a Taylor series expansion of each component in terms of the field can be formulated. Coefficients of such expansions have been calculated for the 1H and 19F nuclei of HF and the 13C and 19F nuclei of CH3F. The calculations have been carried out at the SCF level with moderately large basis sets. The resulting coefficients (a) are the first ab initio results for the electric field dependence of carbon-13 shielding and (b) permit the first comparison of ab initio results for the electric field dependence of 19F shielding in two molecules. The 19F coefficients are found to be quite different for the two molecules—especially at quadratic level. The 13C coefficients are smaller than the 19F coefficients for the CH3F molecule. © 1990 Taylor & Francis Ltd.