Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA.
J Am Soc Mass Spectrom. 2013 Apr;24(4):469-80. doi: 10.1007/s13361-012-0543-3. Epub 2013 Jan 24.
The reactivity of the three distonic isomers of the pyridine radical cation toward tetrahydrofuran is compared in solution and in the gas phase. In solution, the distonic ions were generated by UV photolysis at 300 nm from iodo-precursors in acidic 50:50 tetrahydrofuran/water solutions. In the gas phase, the ions were generated by collisionally activated dissociation (CAD) of protonated iodo-precursors in an FT-ICR mass spectrometer, as described in the literature. The same major reaction, hydrogen atom abstraction, was observed in solution and in the gas phase. Attempts to cleave the iodine atom from the 2-iodopyridinium cation in the gas phase and in solution yielded the 2-pyridyl cation in addition to the desired 2-dehydropyridinium cation. In the gas phase, this ion was ejected prior to the examination of the desired ion's chemical properties. This was not possible in solution. This study suggests that solvation effects are not significant for radical reactions of charged radicals. On the other hand, the even-electron ion studied, the 2-pyridyl cation, shows substantial solvation effects. For example, in solution, the 2-pyridyl cation forms a stable adduct with tetrahydrofuran, whereas in the gas phase, only addition/elimination reactions were observed.
比较了吡啶自由基阳离子的三种离域异构体在溶液中和气相中的与四氢呋喃的反应性。在溶液中，通过在 300nm 处用碘前体在酸性 50:50 四氢呋喃/水溶液中进行 UV 光解生成离域离子。在气相中，通过碰撞活性解离 (CAD) 在 FT-ICR 质谱仪中从质子化的碘前体生成离子，如文献中所述。在溶液中和气相中均观察到相同的主要反应，即氢原子的攫取。试图在气相中和溶液中将碘原子从 2-碘代吡啶鎓阳离子中切断，除了所需的 2-脱水吡啶鎓阳离子外，还生成了 2-吡啶阳离子。在气相中，在检查所需离子的化学性质之前，该离子被逐出。在溶液中这是不可能的。这项研究表明，溶剂化效应对带电自由基的自由基反应没有显著影响。另一方面，所研究的等电子离子，即 2-吡啶阳离子，显示出显著的溶剂化效应。例如，在溶液中，2-吡啶阳离子与四氢呋喃形成稳定的加合物，而在气相中，仅观察到加成/消除反应。
