0000000001312378
AUTHOR
A. Puszko
1H, 13C and 15N NMR study of 2-alkylnitrosoamino-4-nitropyridines and N-oxides: An example on restricted inversion of sp3 nitrogen
Abstract The 1 H, 13 C and 15 N NMR chemical shifts of seven 2-alkylnitrosoamino-4-nitropyridines and seven 2-alkylnitrosoamino-4-nitropyridine N -oxides have been assigned. The GIAO/DFT 13 C chemical shifts of energetically optimized structures have been calculated. The results were compared to the chemical shifts of previously studied 2-alkylamino and 2-alkylnitramino derivatives of 4-nitropyridine and 4-nitropyridine N -oxide. In sterically crowded ortho -substituted congener (2-ethylnitrosoamino-3-methyl-4-nitropyridine N -oxide) restricted inversion of pyramidal amino nitrogen forms a chiral center in the molecule and makes the geminal protons of N–CH 2 -moiety diastereotopic. In 5- an…
1H, 13C and 15N NMR spectral and theoretical studies of some methyl and alkylamino derivatives of 4-halopyridine N-oxides
Abstract Nine new and three earlier known 4-halogen (Cl and Br) substituted pyridine N-oxides have been prepared and their 1 H, 13 C and 15 N NMR chemical shifts assigned based on PFG 1 H, X (X= 13 C and 15 N) HMQC and HMBC experiments as well as the comparison with our earlier results for substituted pyridine N-oxide derivatives. The 15 N resonances of the pyridine nitrogen are 27–40 ppm more shielded in 4-halo-2-alkylamino-6-methyl-5-nitropyridine N-oxide than in parent 4-halopyridine N-oxide. According to quantum chemical ab initio HF/6-311G** calculations the amino tautomer of 4-chloro-2-methylamino-6-methyl-5-nitropyridine N-oxide is more stable than its imino form. Using B3LYP/6-311G*…
Multinuclear 1H, 13C and 15N NMR study of some substituted 2-amino-4-nitropyridines and their N-oxides.
1H, 13C and 15N NMR chemical shift assignments based on pulsed field gradient selected PFG 1H,X (X = 15C and 15N) HMQC and HMBC experiments are reported for three 4-nitropyridine N-oxides and four 4-nitropyridines. It was found that an ortho effect of a methyl group inhibits the deshielding effect of the 4-nitro group and that this effect and the so-called back donation is influenced by electronegativity and position of substituents in the multisubstituted pyridine N-oxides. The shielding effect of N-oxide group is most pronounced in the 15N NMR chemical shifts of the studied compounds. This effect is further modified by methylamino, methylnitramino, 5- or 3-methyl and 4-nitro groups. Among…
Synthesis and NMR characterization of seven new substituted pyridine N-oxides
Abstract Seven 3-substituted (alkylamino, alkylnitramino and alkylnitrosoamino) derivatives of pyridine N-oxide have been prepared and their 1H, 13C and 15N NMR chemical shifts assigned based on PFG 1H, 13C HMQC and PFG 1H, X (X = 13C or 15N) HMBC experiments. In the sterically most crowded congener, 3-ethylnitramino-4-nitropyridine N-oxide, chemical non-equivalence or diastereotopicity of the N–CH2 protons was observed probably due to the chirality of the adjacent amino nitrogen caused by its restricted inversion. The coalescence temperature for the 1H NMR chemical shifts of these geminal protons has been determined and the corresponding ΔG∗ for the energy barrier of the dynamic process ha…
CCDC 185047: Experimental Crystal Structure Determination
Related Article: K.Laihia, E.Kolehmainen, E.Virtanen, M.Nissinen, A.Puszko, Z.Talik|2003|Magn.Reson.Chem.|41|721|doi:10.1002/mrc.1224