Translational diffusion of a carbene and radicals derived from carbenes
Translational diffusion of a carbene and radicals derived from carbenes
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卡宾和卡宾衍生自由基的平移扩散
DOI：
10.1039/ft9969202361
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
Yukimi Akimoto
中科院分区：
文献类型：
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作者：
M. Terazima;H. Tomioka;Katsuyuki Hirai;Y. Tanimoto;Y. Fujiwara;Yukimi Akimoto
用瞬时光栅法测定了重氮化合物在苯中激光光解后，持久性卡宾(六氯二苯基卡宾)和前驱物(2，2′，4，4′，6，6′-hexachlorodiphenyldiazomethane)的平移扩散常数(D)。发现卡宾的D比母体分子的D反常地(大约五倍)小。同时，研究了一些短命卡宾(二苯卡宾、荧叉、α-和β-)在不同溶剂(环己烷、甲醇和乙腈)中的热重信号。在甲醇中，观察到布居格栅信号的单调衰变，并根据速率常数确定了前驱体重氮化合物的D。在环己烷中，上升和下降信号被观察到作为TG信号，这些成分被解释为重氮化合物和卡宾通过从溶剂中吸氢而产生的自由基的扩散。自由基的DS通常比母体分子的DS小3-4倍。瞬时自由基的D值越小，表明扩散过程中自由基的摩擦越大，与基质的摩擦起源于自由基与周围分子之间具有吸引力的分子间相互作用。结果表明，卡宾与基质之间的分子间相互作用强于自由基与基质之间的相互作用。这可能进一步证明未成对电子在溶液中扩散过程中的重要作用。
Translational diffusion constants (D) of a persistent carbene (hexachlorodiphenylcarbene) and, simultaneously, that of the precursor compound (2,2′,4,4′,6,6′-hexachlorodiphenyldiazomethane) are determined, after the laser photolysis of the diazo-compound in benzene, by using the transient grating (TG) method. D of the carbene is found to be anomalously (ca. five times) smaller than that of the parent molecule. At the same time, the TG signals of some short-lived carbenes (diphenylcarbene, fluorenylidene, α-(and β-)naphthylphenylcarbene) are investigated in various solvents (cyclohexane, methanol and acetonitrile). In methanol, monotonic decays of the population grating signals are observed and, from the rate constants, Ds of the precursors, diazo-compounds, are determined. In cyclohexane, rise and decay signals are observed as the TG signal and these components are interpreted in terms of the diffusion of the diazo compounds and radicals created from the carbenes by hydrogen abstraction from the solvents. Ds of the radicals are generally three–four times smaller than those of the parent molecules. The smaller Ds of the transient radicals indicate a larger friction of the radicals during the diffusion process and the origin of the friction with the matrix is attributed to an attractive intermolecular interaction between the radicals and the surrounding molecules. From these results, it is concluded that the intermolecular interaction between the carbene and the matrix is stronger than that between the radicals and the matrix. This could be further evidence for the important role of the unpaired electron in diffusion processes in solution.
H.Tomioka：“2,2, 4,4, 6,6-六溴二苯基卡宾。低温流体溶液中第一个稳定的三线态卡宾，室温下呈晶态”J.Am.Chem.Soc.117。
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