Schröder Detlef, Schwarz Helmut, Milko Petr, Roithová Jana
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo namesti 2, 16610 Praha 6, Czech Republic.
J Phys Chem A. 2006 Jul 13;110(27):8346-53. doi: 10.1021/jp056962f.
The structures of C(7)H(9)(+) ions generated by protonation of toluene are investigated by means of gas-phase infrared spectroscopy in conjunction with labeling experiments and complementary mass spectrometric studies. In full consistency with previous studies, the unimolecular as well as the multiphoton-induced dissociation of mass-selected C(7)H(9)(+) ions lead to losses of molecular hydrogen and methane. Labeling data clearly imply the occurrence of skeletal rearrangements of protonated toluene to isomeric structures in the course of fragmentation. Complementary reactivity studies indicate, however, that the C(7)H(7)(+) ions generated upon dehydrogenation of C(7)H(9)(+) bear the benzylium structure, rather than that of the more stable tropylium ion. Combination of labeling data and extensive theoretical studies lead to a scheme for the fragmentation of protonated toluene, which can account for all experimental findings reasonably well. As far as infrared spectroscopy of gaseous ions is concerned, the present results confirm the structural predictions derived from theory and provide evidence for the existence of protonated cycloheptatriene but also pose some questions about the comparability of intensities in multiphoton dissociation and linear absorption spectra.
通过气相红外光谱结合标记实验和补充质谱研究，对甲苯质子化产生的C(7)H(9)(+)离子的结构进行了研究。与先前的研究完全一致，质量选择的C(7)H(9)(+)离子的单分子以及多光子诱导解离导致分子氢和甲烷的损失。标记数据清楚地表明，在碎片化过程中，质子化甲苯会发生骨架重排形成异构结构。然而，补充反应性研究表明，C(7)H(9)(+)脱氢生成的C(7)H(7)(+)离子具有苄基结构，而不是更稳定的环庚三烯正离子结构。标记数据与广泛的理论研究相结合，得出了质子化甲苯的碎片化方案，该方案能够较好地解释所有实验结果。就气态离子的红外光谱而言，目前的结果证实了从理论推导的结构预测，并为质子化环庚三烯的存在提供了证据，但也对多光子解离和线性吸收光谱中强度的可比性提出了一些问题。
