Author:
Kotowycz G.,Schaefer T.,Bock E.
Abstract
Proton shifts relative to internal benzene of pyridine hydrochloride, hydrobromide, and hydriodide in methylene chloride, acetonitrile, nitromethane, and formic acid are reported. A model involving a hydrogen-bonded ion pair between the pyridinium cation and the counterion is discussed. It is assumed that the counterion reduces considerably the π-electron polarization in the pyridinium ion calculated for the isolated ion by the V.E.S.C.F. method. If the electric fields arising from the π-electrons, the counterion, and the positive charge in the N—H+ sigma bond are taken into consideration, the observed order of the C—H proton shifts is predicted. The N—H+ proton shifts are sensitive to the counterion, the solvent, and traces of water. In formic acid the N—H+ proton shifts of the hydrochloride and hydrobromide are characteristic of the solvent only. In these two cases the N—H+ proton does not exchange rapidly and an 14N—H+ coupling constant of 67.6 ± 0.5 c/s is found.
Publisher
Canadian Science Publishing
Subject
Organic Chemistry,General Chemistry,Catalysis
Cited by
52 articles.
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