A nuclear magnetic resonance investigation of three solid benzenes
A nuclear magnetic resonance investigation of three solid benzenes
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三种固体苯的核磁共振研究
DOI：
10.1098/rspa.1953.0123
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发表时间：
1953
期刊：
影响因子：
--
通讯作者：
R. G. Eades
中科院分区：
文献类型：
--
作者：
E. R. Andrew;R. G. Eades
在75 - 278° K之间，测量了三种多晶苯同位素的质子的核磁共振吸收谱和自旋-晶格弛豫时间。这3种化合物分别为C6 H6、C6 H5 D和1. 3. 5 - C6H3D3。对于所有三种物质，测量的光谱具有低于90° K的完全刚性晶格宽度。一种分析方法的开发，这使得有可能分别获得分子内和分子间的贡献的光谱的二阶矩（均方宽度）从测量的二阶矩，而不需要知道的晶体结构。由分子内贡献发现C_6H_6分子中相邻质子的间距为2.495 ± 0.018 π。分子间的贡献是在协议从晶体结构的知识计算出的值。当温度从90 °K升高到120°K时，这三个物种的光谱都明显变窄。从120°K到熔点（278.7° K），二阶矩几乎保持不变。二阶矩分离程序也适用于在这个范围内，并导致的结论是，缩小是由分子的重新取向，在晶格中的六轴。对自旋-晶格弛豫时间测量的分析表明，对于所有三种物质，重取向过程由3.7 ± 0.2 kcal/mole的活化能控制。再取向频率在85° K时约为104 c/s，在熔点以下上升到1011 c/s。本文讨论了固体苯的拉曼光谱与目前实验结果之间的关系。最后，考虑到应用到其他材料的方法分离内和分子间的贡献的二阶矩。
The nuclear magnetic resonance absorption spectrum and the spin-lattice relaxation time have been measured for the protons in three isotopic species of benzene in polycrystalline form between 75 and 278° K. The three species were C6H6, C6H5D and 1. 3. 5 - C6H3D3. For all three species the measured spectrum has its full rigid lattice width below 90° K. A method of analysis is developed which makes it possible to derive separately the intramolecular and the intermolecular contributions to the second moment (mean square width) of the spectrum from the measured second moments, without the necessity of knowing the crystal structure. From the intramolecular contribution it is found that the separation of neighbouring protons in the C6H6 molecule is 2.495 ± 0.018 Å. The intermolecular contribution is in agreement with a value calculated from a knowledge of the crystal structure. On warming from 90 to 120°K the spectrum for all three species narrows considerably. From 120°K to the melting-point (278.7° K) the second moments remain almost constant. The second moment separation procedure is also applied in this range and leads to the conclusion that the narrowing is caused by reorientation of the molecules about their hexad axes in the crystal lattice. Analysis of the measurements of the spin-lattice relaxation time shows that for all three species the reorientation process is governed by an activation energy of 3.7 ± 0.2 kcal/mole. The reorientation frequency is of the order of 104 c/s at 85° K and rises to a value of the order of 1011 c/s just below the melting-point. The relationship between the present experimental results and recent measurements of the Raman spectrum of solid benzene is discussed. Finally, consideration is given to the application to other materials of methods of separating the intra- and intermolecular contributions to the second moment.