GIAO/DFT calculated chemical shifts of tautomeric species. 2-Phenacylpyridines and (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines

H-1, C-13 and N-15 NMR chemical shifts for 28 substituted 2-phenacylpyridines (ketimine forms) and their enolimine tautomers, (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines were calculated via the GIAO/DFT approach. Among four tested methods at the B3LYP level of theory, the 6-311G, 6-311++G and 6-311G** basis sets gave acceptable result for 13C NMR chemical shifts whereas the 6-311++G** basis set was the minimum needed for reproduction of N-15 NMR chemical shifts. Satisfactory reproduction of C-13 and N-15 NMR chemical shifts for different tautomers revealed that intramolecular hydrogen bonding could be modeled reliably by these calculations when the geometry optimizations were done with the HF/3-21G method. Agreements between theoretical and experimental C-13 and N-15 NMR chemical shifts and also HF/3-21G and HF/6-31G** optimized structural parameters with those obtained by x-ray crystallographic measurements suggests that it is not necessary to select too sophisticated and CPU time-intensive methods for geometry optimizations. Copyright (C) 2001 John Wiley & Sons, Ltd.