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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >An Investigation of the Dynamic and Conformational Properties of Alkylcyclohexanes Absorbed in Siliceous Zeolite ZSM-5
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An Investigation of the Dynamic and Conformational Properties of Alkylcyclohexanes Absorbed in Siliceous Zeolite ZSM-5

机译：硅质沸石ZSM-5吸收的烷基环己烷的动力学和构象性质的研究

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摘要

The dynamic and conformational behavior of three related alkylcyclohexane molecules, cyclohexane (CH), methylcyclohexane (MCH), and trans-1,4-dimethylcyclohexane (DMCH), loaded within completely siliceous zeolite ZSM-5 has been investigated by variable temperature FT-Raman spectroscopy. Our results indicate that at room temperature CH molecules inside the ZSM-5 framework undergo significant reorientational motions around different axes as well as ring inversion and that the reorientational motions have ceased when the temperature is lowered to 153 K. For MCH and DMCH, in contrast, the major molecular motions are removed upon initial loading into the ZSM-5 framework. At low temperatures, the symmetry of CH inside ZSM-5 clearly deviates from the perfect D_(3d) symmetry of the free molecule. At room temperature, the conformational equilibrium of MCH guest molecules still exists in the ZSM-5 host, but at low temperatures, MCH adopts the equatorial conformation exclusively. Interestingly, for DMCH absorption into ZSM-5 results in an increase in the population of the high-energy, small-volume diaxial conformer. The low-temperature Raman spectra of the ZSM-5 framework have also shown that for CH/ZSM-5 and MCH/ZSM-5 complexes, the zeolite framework is not rigid and undergoes significant thermal motion at room temperature. For DMCH/ZSM-5, the zeolitic framework also undergoes thermal motion, but there is a larger distribution of Si-O-Si angles.
机译：通过变温FT-拉曼光谱研究了负载在完全硅质沸石ZSM-5中的三个相关烷基环己烷分子，环己烷（CH），甲基环己烷（MCH）和反式1,4-二甲基环己烷（DMCH）的动力学和构象行为。光谱学。我们的结果表明，在室温下，ZSM-5框架内的CH分子会围绕不同的轴进行显着的方向运动以及环反转，并且当温度降低到153 K时，方向运动也就停止了。相比之下，对于MCH和DMCH ，最初加载到ZSM-5框架后，主要的分子运动就被消除了。在低温下，ZSM-5内部CH的对称性明显偏离了自由分子的完美D_（3d）对称性。在室温下，ZCH-5主体中仍存在MCH客体分子的构象平衡，但在低温下，MCH仅采用赤道构象。有趣的是，对于DMCH，吸收到ZSM-5中会导致高能量，小体积双轴构象异构体的增加。 ZSM-5骨架的低温拉曼光谱还表明，对于CH / ZSM-5和MCH / ZSM-5配合物，沸石骨架不是刚性的，并且在室温下会经历明显的热运动。对于DMCH / ZSM-5，沸石骨架也经历热运动，但Si-O-Si角分布较大。

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