6533b7ddfe1ef96bd1275231

RESEARCH PRODUCT

1H, 13C and 15N NMR study of 2-alkylnitrosoamino-4-nitropyridines and N-oxides: An example on restricted inversion of sp3 nitrogen

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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- and 6-CH 3 -substituted derivatives this diastereotopism disappears, but the rotation around N–CH 2 sigma bond in all congeners is so slow in NMR time scale, that 1 H, 13 C and 15 N NMR chemical shifts could be detected for two conformers. In 4-nitropyridine and 4-nitropyridine N -oxide derivatives the shielding of aromatic nitrogen is very sensitive to the ring substituents. 2-Alkylnitrosoamino group produces a significant shielding based on conjugation between the ring and the nitrosoamino group.