Wu Haiming, Yuan Chengqian, Zeng Chenghui, Luo Zhixun
State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China.
University of Chinese Academy of Sciences, Beijing 100049, P. R. China.
ACS Omega. 2018 Sep 6;3(9):10743-10747. doi: 10.1021/acsomega.8b01840. eCollection 2018 Sep 30.
Utilizing customized deep-ultraviolet laser ionization mass spectroscopy, here we report a finding of remarkable dehydrogenation product of ,-dimethyl--toluidine (DMT). The DMT dehydrogenates find comparable mass abundance with the DMT molecule ions showing decent stability at the loss of one electron and one H atom from the DMT molecule. First-principles calculation reveals that the dehydrogenation most readily occurs at the N-connected methyl group. Furthermore, at the removal of a hydrogen atom, a neighboring hydrogen atom on the other methyl come close and interact with the dehydrogenated methylene group, pertaining to C-H···C weak interactions which give rises to a resonant structure (C···H-C) on a basis of hydrogen atom quantum tunneling effect. The quantum tunneling tautomer of DMT dehydrogenates displays reversible donor-acceptor charge-transfer interactions as demonstrated by natural bonding orbital analysis and vibrational spectroscopy. It is worth noting that the novel dehydrogenation product was also observed for another small organic molecule -phenylenediamine, which bears two neighboring amino groups and the subsequent dehydrogenation product pertains to resonant structures of N-H···N and N···H-N. The deep ultraviolet laser not only produces fragmentation-free mass spectra for such small organic molecules but also tailors the interesting quantum tunneling tautomer from such specific molecules.
利用定制的深紫外激光电离质谱，我们在此报告了对N,N-二甲基-对甲苯胺（DMT）显著脱氢产物的一项发现。DMT的脱氢产物与DMT分子离子具有相当的质量丰度，显示出在从DMT分子失去一个电子和一个氢原子时具有相当的稳定性。第一性原理计算表明，脱氢最容易发生在与氮相连的甲基上。此外，在去除一个氢原子时，另一个甲基上的相邻氢原子会靠近并与脱氢的亚甲基相互作用，这属于C-H···C弱相互作用，基于氢原子量子隧穿效应产生了一种共振结构（C···H-C）。通过自然键轨道分析和振动光谱证明，DMT脱氢产物的量子隧穿互变异构体表现出可逆的供体-受体电荷转移相互作用。值得注意的是，在另一种带有两个相邻氨基的小分子有机化合物对苯二胺中也观察到了这种新型脱氢产物，其随后的脱氢产物属于N-H···N和N···H-N的共振结构。深紫外激光不仅为此类小分子有机化合物产生无碎片质谱，还能从此类特定分子中定制出有趣的量子隧穿互变异构体。
