Abstract
AbstractThe nuclear magnetic resonace spectra of six pyridocyanines, four azapyridocyanines, one monoquaternized 2,4′‐dipyridylamine and two dipyridylamines were measured and fully analyzed. The spectra of the 2,2′‐pyrido‐ and azapyridocyanines support previously published results that these dyes exist in the all‐trans form and not in the mono‐cis form, as stated by others. Strong evidence was obtained that N,N′‐ethylene‐2,2′‐pyridocyanine is twisted. The spectra of dyes with p‐connected pyridine rings indicate that these nuclei may rotate around the bond between the meso group and the p‐position. Relative chemical shifts in the spectra of the homologous pyrido‐ and azapyridocyanines can be explained by electronic effects rather than by magnetic anisotropy of the aza group or changes in ring currents.
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