15N NMR Chemical Shifts for the Identification of Dipyrrolic Structures.
Wood, Tabitha E.
Beshara, Cory S.
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A variety of dipyrromethanes and dipyrromethenes have been prepd., and their 15N NMR chem. shifts have been measured by two-dimensional correlation to 1H NMR signals. The nitrogen atoms in five examples of dipyrromethanes consistently exhibit chem. shifts around -231 ppm, relative to nitromethane. Seven examples of hydrobromide salts of meso-unsubstituted dipyrromethenes consistently display 15N chem. shifts around -210 ppm, while their corresponding zinc(II) complexes exhibit chem. shifts around -170 ppm. The presence of electron-withdrawing substituents on one of the pyrrolic rings of dipyrromethenes affects the chem. shifts of both of the nitrogen nuclei in the mol. Boron difluoride complexes of meso-unsubstituted dipyrromethenes display 15N chem. shifts around -190 ppm. Two examples of free-base dipyrromethenes bearing substituents at the meso-position exhibit 15N chem. shifts at approx. -156 ppm, and for the zinc complexes of these compds. at -162 ppm. One-bond nitrogen-hydrogen coupling consts., when measurable, were consistently in the range of -96 Hz. Since the measured 15N chem. shifts have such a high regularity correlated to structure, they can be used as diagnostic indications for identifying the structure of dipyrrolic compds. [on SciFinder(R)]
Wood, Tabitha E., Bob Berno, Cory S. Beshara, and Alison Thompson. 2006. "15N NMR Chemical Shifts for the Identification of Dipyrrolic Structures.." Journal of Organic Chemistry 71(8): 2964-2971.