Self-consistent Perturbation Theory of 13C magnetic resonance parameters in pyridines

The ¹³C chemical shifts for pyridine and 22 of its monosubstituted derivatives, the ¹³C? ¹⁹F couplings for fluoropyridines and the ¹³C? ¹⁵N couplings for pyridine, the pyridinium cation and pyridine-N-oxide have been calculated using the SCF-INDO Finite Perturbation Theory. Experimental ¹³C chemical shifts show only modest correlation with calculated shieldings; trends and magnitudes are, however, reasonably reproduced in some cases. Theory yields a correct account of the magnitudes, signs and trends for the various couplings except for ²J(CF). Addition of an empirical correction of + 33.5 Hz to the Fermi contact term leads also to excellent reproduction of this coupling.