Proton tautomerism in 2-nitramino-C-nitropyridine derivatives - Experimental and quantum chemical study

Add time:08/07/2019    Source:sciencedirect.com

The structures of 2-nitramino-3-nitropyridine and 2-nitramino-5-nitropyridine have been characterized by X-ray diffraction and Density Functional Theory (DFT) studies. In the crystals, both compounds exist as the imino forms. The DFT calculations were performed in order to explore the amino-imino tautomerism of the studied compounds in the gas phase and the influence of solvent polarity on the tautomeric equilibrium. The Harmonic Oscillator Model of Aromaticity index (HOMA) and Nucleus Independent Chemical Shift (NICS) calculated for the pyridine rings of the studied systems, demonstrated a noticeable decrease in aromaticity of the imino forms. This study showed also that the higher stability of the tautomeric states could be observed for the systems with the intramolecular hydrogen bonds, which contribute to the formation of six-membered quasi-rings.

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