HF–DFT calculations of 14N and 35Cl quadrupole coupling constants on optimized molecular structures of pyridine and the monochloropyridines

Abstract

14N and 35Cl nuclear quadrupole coupling constants in the monochloropyridines and 14N in pyridine have been determined in the principal axes of both the inertia and coupling constant tensors by HF–DFT calculations of the molecular electric field gradients on B3P86/6-31G(3d,3p) optimized molecular structures.In the case of 4-chloropyridine, the calculated 14N coupling constants are probably more accurate than the experimental values.Investigation of the substitution effect shows that the differences in nitrogen nqccs between 2-chloropyridine and pyridine are largely due to the presence of the chlorine substituent (as opposed to distortion of the ring). The small differences found in 3-chloropyridine can be understood as due to near cancellation of effects due to the substituent and ring distortion. In 4-chloropyridine, on the other hand, these effects are additive, accounting for the differences for this molecule.