Büker Heinz-Hermann, Grützmacher Hans-Friedrich
Fakultät für Chemie, Universität Bielefeld, Bielefeld, Germany.
Eur J Mass Spectrom (Chichester). 2017 Dec;23(6):327-340. doi: 10.1177/1469066717729537. Epub 2017 Sep 8.
The reactions of the [2-2]-paracyclophane 1 and the [2-2]-metaparacyclopane 2 in the gas phase after protonation by CI(CH) or CI(I-CH) were studied by FT-ICR mass spectrometry. The ions CH produced in the external ion source of the FT-ICR instrument were transferred into the ICR cell containing the neutral reactant, and the reactions were analyzed measuring the efficiency of the transfer of a proton to a series of bases with known proton affinity and gas phase basicity as well as the efficiency of the ion-molecule reaction with ethyl vinyl ether. Both reaction types show that the ions CH produced by chemical ionization (CI) consist of two sets of isomeric ions A and B which exhibit distinctly different behavior on deprotonation and of the reaction with ethyl methyl ether. Isomer(s) A (about 65% of the ion population) react efficiently with this vinyl ether by an addition/elimination process typical of primary and secondary benzylic carbenium ions, while isomer B (about 35% of the ion population) undergoes only an ineffective deprotonation by the vinyl ether. By bracketing deprotonation, it is shown that A is actually composed of two isomers A and A with slightly different proton affinity and gas phase basicity. These two ions have been identified using CA-mass spectrometry as protonated 3-phenethylstyrene (A) and protonated 4-phenethylstyrene (A). The CA-mass spectrum of the isomer B indicated that these ions CH correspond to protonated 1-(ethyl phenyl)-1-phenyl-ethene. This agrees with the rather strong basicity of the conjugated base of ions B, which results in a slow deprotonation. A protonated 1-(ethyl phenyl)-1-phenyl-ethene can arise from a protonated 2-phenethylstyrene by H- and subsequent phenyl shifts, but requires the preceding rearrangement of the protonated [2.2]-paracyclophane into the protonated isomer "[2.2]-orthocyclophane" - the 1,5-dibenzocyclooctadiene. The possibility of such a deep-sited rearrangement was studied by the computation of the relevant reaction routes applying DFT-methods at the level B3LYP/6-311+g(3d,2p)//B3LYP/3-21g) to analyze the reaction mechanisms.
通过傅里叶变换离子回旋共振质谱法（FT-ICR MS）研究了[2.2]对环芳烷1和[2.2]间环芳烷2在气相中被CI(CH)或CI(I-CH)质子化后的反应。在FT-ICR仪器的外部离子源中产生的离子CH被转移到含有中性反应物的ICR池中，通过测量质子转移到一系列具有已知质子亲和能和气相碱度的碱上的效率以及与乙基乙烯基醚的离子-分子反应效率来分析反应。两种反应类型均表明，化学电离（CI）产生的离子CH由两组异构离子A和B组成，它们在去质子化和与乙基乙烯基醚反应时表现出明显不同的行为。异构体A（约占离子总数的65%）通过典型的伯和仲苄基碳正离子的加成/消除过程与这种乙烯基醚高效反应，而异构体B（约占离子总数的35%）仅通过乙烯基醚进行无效的去质子化。通过括弧去质子化表明，A实际上由两种质子亲和能和气相碱度略有不同的异构体A和A组成。使用CA质谱法已将这两种离子鉴定为质子化的3-苯乙基苯乙烯（A）和质子化的4-苯乙基苯乙烯（A）。异构体B的CA质谱表明，这些离子CH对应于质子化的1-(乙基苯基)-1-苯基乙烯。这与离子B的共轭碱相当强的碱度一致，这导致去质子化缓慢。质子化的1-(乙基苯基)-1-苯基乙烯可由质子化的2-苯乙基苯乙烯通过H-和随后的苯基迁移产生，但需要质子化的[2.2]对环芳烷先重排为质子化的异构体“[2.2]邻环芳烷”——1,5-二苯并环辛二烯。通过应用DFT方法在B3LYP/6-311+g(3d,2p)//B3LYP/3-21g水平计算相关反应路径来研究这种深度重排的可能性，以分析反应机理。
