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Experimental and theoretical studies of the energetics of gas-phase organic cluster ions.

机译：气相有机簇离子能量的实验和理论研究。

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摘要

Mass spectrometry was used in combination with theoretical calculations and statistical rate theories to probe both the unimolecular dissociation and isomerization characteristics of proton-bound molecular pairs. These proton-bound pairs have been found to dissociate by simple hydrogen bond cleavage or rearrange via a unimolecular SN2 mechanism to form an isomeric complex that loses water. The proton-bound pair rearranges to an intermediate ion complex (IC) via TSa followed by the formation of the thermodynamically stable isomer that loses water via TSb. Empirical relationships based on the number of stabilizing alkyl groups on the central SN2 carbon and differences in proton affinities have been developed for estimating the energies of the two transition states (TSa and TSb) and IC in the isomerization reaction.; The entropy of activation, DeltaS‡, for the dissociation of the proton-bound pairs to CH3CNH+ and ROH was found to change systematically with molecular functionality, with the entropy decreasing from 70 J K-1 mol-1 in (CH3 CN)(CH3OH)H+ to 6 J K-1 mol -1 in (CH3CN)((CH3)2CHOH)H +. This systematic change was not observed in the dissociation to CH3CN and ROH2+ or in the thermodynamic entropy change for the dissociation. The entropies of activation for the competing dissociation channels for (CH3CN)(CH3OH)H+ and (CH3CN)(CH3CH2OH)H+ were the same within error and thus Delta(DeltaS‡) ≈ 0 while this value ranged from 40-45 J K-1 mol -1 for the propanol-containing pairs. The Delta(DeltaS) for all four proton-bound pairs was zero.; The unimolecular dissociation of the series of (NO)(A)+ cluster ions (where A = benzene, pyridine, furan, thiophene and benzonitrile) was examined using tandem mass spectrometry and evidence was found for the participation of excited states in their dissociation. The unimolecular dissociation of metastable ionic complexes generated by NO chemical ionization of benzonitrile changes as a function of ion source pressure. As the NO concentration in the source increases, the metastable ion (MI) mass spectrum goes from being dominated by NO+ to one dominated by ionized benzonitrile and its fragmentation products. A similar result is observed when A = pyridine. When A = benzene, the MI mass spectrum is dominated by the ionized aromatic, a result that is consistent with the adiabatic dissociation of the ground singlet-state of the complex. The MI mass spectra of the complexes involving furan and thiophene are consistent with the dissociation of the lowest energy singlet-state.
机译：质谱与理论计算和统计速率理论结合使用，以探测质子结合分子对的单分子解离和异构化特征。已发现这些质子结合对可通过简单的氢键裂解而解离，或通过单分子SN2机制重排形成失去水分的异构体。质子结合对通过TSa重排为中间离子络合物（IC），然后形成热力学稳定的异构体，该异构体通过TSb失水。已经开发了基于中心SN 2碳上稳定烷基的数目和质子亲和力差异的经验关系，以估计异构化反应中两个过渡态（TSa和TSb）和IC的能量。发现质子结合对解离为CH3CNH +和ROH的激活熵DeltaS‡随分子功能的变化而系统地变化，熵从（CH3 CN）（CH3OH）的70 J K-1 mol-1降低）H +到（CH3CN）（（CH3）2CHOH）H +中的6 J K-1 mol -1。在与CH3CN和ROH2 +的解离中或在该解离的热力学熵变中均未观察到这种系统性变化。 （CH3CN）（CH3OH）H +和（CH3CN）（CH3CH2OH）H +的竞争解离通道的激活熵在误差内相同，因此Delta（DeltaS‡）＆ap; 0，而含丙醇对的值范围为40-45 J K-1 mol -1。所有四个质子结合对的Delta（DeltaS）为零。使用串联质谱法检测了一系列（NO）（A）+簇离子（其中A =苯，吡啶，呋喃，噻吩和苄腈）的单分子解离，发现了激发态参与其解离的证据。由苄腈的NO化学电离产生的亚稳离子络合物的单分子解离随离子源压力的变化而变化。随着源中NO浓度的增加，亚稳态离子（MI）质谱图由NO +为主，变为离子化苄腈及其碎片化产物为主。当A ＝吡啶时，观察到相似的结果。当A =苯时，MI质谱以离子化的芳族化合物为主，这一结果与配合物的基态单重态的绝热解离相符。涉及呋喃和噻吩的配合物的MI质谱与最低能量单重态的解离相一致。

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  • 作者

    Grabowy, Julie Ann Douglas.;

  • 作者单位

    University of Ottawa (Canada).;

  • 授予单位 University of Ottawa (Canada).;
  • 学科 Chemistry Organic.
  • 学位 Ph.D.
  • 年度 2005
  • 页码 267 p.
  • 总页数 267
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 有机化学;
  • 关键词

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