Molecular structure and electron distribution of 4-nitropyridine N-oxide: Experimental and theoretical study of substituent effects.
J Mol Struct, 2020/10/05;1217:128476.
Belova NV[1], Pimenov OA[1], Kotova VE[1], Girichev GV[1]
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PMID: 32427177DOI: 10.1016/j.molstruc.2020.128476
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Abstract
The molecular structure of 4-nitropyridine N-oxide, 4-NO2-PyO, has been determined by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and by quantum chemical calculations (DFT and MP2). Comparison of these results with those for non-substituted pyridine N-oxide and 4-methylpyridine N-oxide CH3-PyO, demonstrate strong substitution effects on structural parameters and electron density distribution. The presence of the electron-withdrawing -NO2 group in para-position of 4-NO2-PyO results in an increase of the ipso-angle and a decrease of the semipolar bond length r(N→O) in comparison to the non-substituted PyO. The presence of the electron-donating -CH3 group in 4-CH3-PyO leads to opposite structural changes. Electron density distribution in pyridine-N-oxide and its two substituted compounds are discussed in terms of natural bond orbitals (NBO) and quantum theory atoms in molecule (QTAIM).
Keywords: Electron density distribution; Gas-phase electron diffraction; Molecular structure; Pyridine-N-oxides; Quantum chemical calculations; Substituent effect
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