Belova Natalya V, Girichev Georgiy V, Kotova Vitaliya E, Korolkova Kseniya A, Trang Nguyen Hoang
Ivanovo State University of Chemistry and Technology, Research Institute for Thermodynamics and Kinetics of Chemical Processes, 153460 Ivanovo, Russia.
Vietnam National University, Hanoi, Vietnam.
J Mol Struct. 2018 Mar 15;1156:210-215. doi: 10.1016/j.molstruc.2017.11.070. Epub 2017 Nov 17.
The molecular structure of 4-methylpiridine-N-oxide, 4-MePyO, has been studied by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and quantum chemical (DFT) calculations. Both, quantum chemistry and GED analyses resulted in molecular symmetry with the planar pyridine ring. Obtained molecular parameters confirm the hyperconjugation in the pyridine ring and the sp hybridization concept of the nitrogen and carbon atoms in the ring. The experimental geometric parameters are in a good agreement with the parameters for non-substituted N-oxide and reproduced very closely by DFT calculations. The presence of the electron-donating CH substituent in 4-MePyO leads to a decrease of the ipso-angle and to an increase of r(N→O) in comparison with the non-substituted PyO. Electron density distribution analysis has been performed in terms of natural bond orbitals (NBO) scheme. The nature of the semipolar N→O bond is discussed.
通过质谱监测的气相电子衍射（GED/MS）和量子化学（DFT）计算研究了4-甲基吡啶-N-氧化物（4-MePyO）的分子结构。量子化学和GED分析均得出吡啶环呈平面状的分子对称性。获得的分子参数证实了吡啶环中的超共轭以及环中氮和碳原子的sp杂化概念。实验几何参数与未取代的N-氧化物的参数吻合良好，并通过DFT计算非常精确地再现。与未取代的PyO相比，4-MePyO中给电子的CH取代基的存在导致本位角减小和r(N→O)增大。根据自然键轨道（NBO）方案进行了电子密度分布分析。讨论了半极性N→O键的性质。
