13C NMR spectra of p-nitrobenzoyl 2-, 4-, and 6-aminopyridine-3-carboxylates, their hydrochlorides, trifluoroacetates and 1-benzyl derivatives were studied. As found from the chemical shifts of pyridine carbon atoms C-2, C-4 and C-6, the free bases exist in the amino form whereas hydrochlorides and 1-substituted pyridinium derivatives in the imino form. Trifluoroacetates of the 2- and 6-amino derivatives have structure similar to that of amidiniumcarboxylates (parallel hydrogen bonds and partially ionic character) whereas trifluoroacetate of the 4-amino derivative is structurally close to the corresponding hydrochloride. The found structures were confirmed by 1H NMR and IR spectroscopy.
Amino-Imino Tautomerism in Derivatives of 2-, 4-and 6-Aminonicotinic Acid.-The title derivatives, e.g. (IIIa), (V), (VI), and (VIII), are investigated with the aid of 13C NMR spectroscopy. The main tantomeric form of the products is determined. Depending on the derivative amino or imino forms are observed. -(SMRCKOVA, S.; JURICOVA, K.; PRUTIANOV, V.; Collect.
Nucleophilic substitution of the nitro group in 4-nitro-3-pyridinecarboxanilide 1-oxide (IIa) afforded 4-hydroxy- (IIb), 4-chloro- (IIc), 4-methoxy- (IId), 4-ethoxy- (IIe), and 4-dimethylamino-3-pyridinecarboxanilide (IIf). The 1H and 13C NMR chemical shifts of the pyridine moiety were correlated with the Hammett constants of the substituent in position 4, with the exception of compound IIb. The reason of this phenomenon is discussed.
Nucleophilic Substitution in a Series of 4-Nitronicotinic Acid 1-Oxide Derivatives.-Nucleophilic substitution of the nitro group in 4-nitronicotinic acid N-oxide (I) or its anilide (IV) affords the 4-hydroxy (III), 4-chloro ( V), 4-methoxy (VIIa), 4-ethoxy (VIIb) and 4-dimethylamino (IX) derivative. -(POHL, R.; PRUTIANOV, V.; SMRCKOVA-VOLTROVA, S.; Collect.
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