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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Time-Resolved Photodissociations of Iodotoluene Radical Cations
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Time-Resolved Photodissociations of Iodotoluene Radical Cations

机译：碘甲苯自由基阳离子的时间分辨光解离

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Unimolecular dissociation of o-, m-, and p-iodotoluene radical cations that yield C_7H_7~+ by loss of an iodine atom have been studied by time-resolved photodissociation (TRPD) spectroscopy using Fourier transformation cyclotron resonance mass spectrometry. Iodotoluene radical cations were prepared by the phoionization charge-transfer (PICT) method. The TRPD spectra were obtained in the wavelength range 480-575 nm. The rate-energy data from the presents wok are combined with the previous rate data obtained in a higher internal energy range to extract activation parameters for unimolecular dissociations. For the direct C-I cleavage channel that leads to tolyl cations, the entropy changes for activation are assumed to be identical to that of the vinylic C-I cleavage of the iodobenzene radical cation, and activation barriers are estimated from thermochemical thresholds. For the lowest barrier rearrangement channel that leads to the benzyl cation, the entropy changes are assumed to be identical to those of the corresponding bromotoluene radical cations. Activation barriers for the rearrangement channel are determined to be 1.77, 1.88, and 1.90 eV for o, m, and p isomers, respectively. Both the product structures and activation parameters for the lowest barrier rearrangement process lead support to the McLaffetry mechanism that invokes the H-atom migration from the α to the ipso- or ortho-carbon site and the subsequent H-atom and/or CH_2 group migration on the ring to form benzyl precursors. The effects of halogen substitution (X = Cl, Br, and I) on the rearrangement process are discussed.
机译：利用傅里叶变换回旋共振质谱通过时间分辨光解离（TRPD）光谱研究了通过丢失碘原子产生C_7H_7〜+的邻，间和对碘甲苯自由基阳离子的单分子解离。碘甲苯自由基阳离子是通过光子化电荷转移（PICT）方法制备的。在480-575nm的波长范围内获得TRPD光谱。来自当前炒锅的速率-能量数据与在较高内部能量范围内获得的先前速率数据组合，以提取用于单分子解离的活化参数。对于导致甲苯基阳离子的直接C-1裂解通道，假设激活的熵变化与碘苯自由基阳离子的乙烯基C-1裂解的熵变化相同，并且可以根据热化学阈值估算激活势垒。对于导致苄基阳离子的最低势垒重排通道，假定熵变与相应的溴甲苯基自由基阳离子的熵变相同。对于o，m和p异构体，重排通道的激活势垒分别确定为1.77、1.88和1.90 eV。最低势垒重排过程的产物结构和激活参数均支持McLaffetry机制，该机制调用H原子从α迁移至ipso或邻碳或邻碳位点，以及随后的H原子和/或CH_2基团迁移在环上形成苄基前体。讨论了卤素取代（X = Cl，Br和I）对重排过程的影响。

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