Multinuclear Magnetic Resonance Study of 2,4,6-Triarylpyridines, 1-Methyl-2,4,6-Triarylpyridinium, and 2,4,6-Triarylpyrylium Cations

Abstract The H, 13C, 15N, and 19F NMR spectra of 2,4,6-triarylpyridines, 1-methyl-2,4,6-triarylpyridinium and 2,4,6-triarylpyrylium perchlorates have been studied. The H NMR signals of protons 3(5) in the heteroaromatic ring are deshielded due to the polarization of C-H bonds caused by delocalization of the positive charge in pyridinium and pyrylium cations. Generally, conformational and structural variations affect the 13C NMR chemical shifts of all carbons in the heteroaromatic ring. Those of carbons 3(5) can best be related to the electron-donating or electron-accepting ability of substituents. However, both electronic character of substituents and charge of heteroatom itself are needed …