title: 15N NMR chemical shifts for the identification of dipyrrolic structures.
abstract: A variety of dipyrromethanes and dipyrromethenes have been prepared, and their 15N NMR chemical shifts have been measured by two-dimensional correlation to 1H NMR signals. The nitrogen atoms in five examples of dipyrromethanes consistently exhibit chemical shifts around -231 ppm, relative to nitromethane. Seven examples of hydrobromide salts of meso-unsubstituted dipyrromethenes consistently display 15N chemical shifts around -210 ppm, while their corresponding zinc(II) complexes exhibit chemical shifts around -170 ppm. The presence of electron-withdrawing substituents on one of the pyrrolic rings of dipyrromethenes affects the chemical shifts of both of the nitrogen nuclei in the molecule. Boron difluoride complexes of meso-unsubstituted dipyrromethenes display 15N chemical shifts around -190 ppm. Two examples of free-base dipyrromethenes bearing substituents at the meso-position exhibit 15N chemical shifts at approximately -156 ppm, and for the zinc complexes of these compounds at -162 ppm. One-bond nitrogen-hydrogen coupling constants, when measurable, were consistently in the range of -96 Hz. Since the measured 15N chemical shifts have such a high regularity correlated to structure, they can be used as diagnostic indications for identifying the structure of dipyrrolic compounds.
authors.affiliation: Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4J3.
authors.forename: Tabitha E
authors.initials: TE
authors.lastname: Wood
authors.forename: Bob
authors.initials: B
authors.lastname: Berno
authors.forename: Cory S
authors.initials: CS
authors.lastname: Beshara
authors.forename: Alison
authors.initials: A
authors.lastname: Thompson