NITROGEN NMR SHIELDINGS OF SOME NITRO DERIVATIVES OF 2-AMINO-4-METHYLPYRIDINE SYSTEMS

Abstract

High precision ¹⁴N NMR shieldings (chemical shifts), bulk susceptibility corrected, are reported for dilute solutions in pure, dry acetone for a group of nitro derivatives of (N-sub-stituted) 2-amino-4-methylpyridines, with nitro substituents in positions either 5 or 3 or both, where at least some of these should reveal serious steric hindrance between the substituents involved. The nitrogen shieldings as well as the corresponding PM3 optimized geometries show quite clearly that the 5-nitro derivatives are planar or nearly planar, without any significant hindrance to the π-conjugation throughout the molecular system concerned, while the 3-nitro derivatives experience deviations from coplanarity of the pyridine ring and the nitro and amino substituents, with concomitant impairment of π-conjugation between these moieties. The nitrogen shieldings of the pyridine nitrogen atoms in N-nitramino-2-alkyl-4-methyl 3 (or 5)-nitropyridines indicate that the N-nitramino group acts as a modest donor of π-electrons, much weaker with respect to the donor strength of amino, alkylamino or phenylamino substituents.

How to Cite
Wandas, M.; Puszko, A.; Biedrzycka, Z.; Witanowski, M. Chem. Heterocycl. Compd. 2004, 40, 747 [Khim. Geterotsikl. Soedin. 2004, 873.]

For this article in the English edition, see DOI 10.1023/B:COHC.0000040770.37574.f1