GIAO/DFT calculated chemical shifts of tautomeric species. 2‐Phenacylpyridines and (<i>Z</i>)‐2‐(2‐hydroxy‐2‐phenylvinyl)pyridines

Abstract

Abstract 1 H, 13 C and 15 N 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 13 C NMR chemical shifts whereas the 6–311++G ** basis set was the minimum needed for reproduction of 15 N NMR chemical shifts. Satisfactory reproduction of 13 C and 15 N 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 13 C and 15 N 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 © 2001 John Wiley &amp; Sons, Ltd.