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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Mechanism of the Major Orientation Polarization in Alcohols, and the Effects of Steric Hindrance-, and Dilution-Induced Decrease on H-Bonding
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Mechanism of the Major Orientation Polarization in Alcohols, and the Effects of Steric Hindrance-, and Dilution-Induced Decrease on H-Bonding

机译：醇中主要取向极化的机理，以及立体阻碍和稀释诱导的降低对氢键的影响

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摘要

To gain insight into the effects of intennolecular H-bond association on the changes in pennittivity and relaxation characteristics of supercooled alcohols, two techniques were used here: (i) introducing a C~5 group in 2-propanol to obtain l-phenyl-2-propanol, and thus increasing the steric hindrance to H-bonding, and (iifdissolving the latter in 2-methylpentane and thus decreasing the extent of H-bonding by separating molecules in a nonpolar solvent. Broad-band dielectric spectroscopy studies of supercooled liquid l-pheny1- 2-propanol and its 1:1 (mol:mol) mixture in 2-methylpentane were perfonned over the 188-238 K range. These show that approx 94% of the total polarization decays according to the Davidson-Cole distribution of relaxation times and that the equilibrium pennittivity decreases when phenyl group is substituted in 2-propanol. Analysis in tenns of,the statistical theories of dielectric behavior shows that the decrease is due to a decrease in the orientation correlation factor, andtfiat this also occurs in the mixture with 2-methylpentane. The induced steric hindrance reduces the extent of intermolecular H-bonding in comparison with that of 2-propanol. The relaxation rate follows the non-Arrhenius t~mperature dependence. It has been examined qualitatively in tenns of the Dyre theory whichconside~s that the apparent Arrhenius energy itself is temperature-dependent, as in the classical iJlterpretations, and quantitatively in tenns of the cooperatively :rearranging region's size, without implying that there'is an underlying thennodynamic transition in its equilibrium liquid. The relaxation rate also fits the power law with the critical exponent of 14.52 for l-phenyl-2-propanol and 12.9 for the mixture, instead of 2 to 4, usually required by the mode-coupling theory .This indicates the ambiguity of the power- law equations. The excess dielectric loss observed at high frequencies may indicate Nagle' s "wing", or else a merged Johari-oldstein relaxation.
机译：为了深入了解分子间H键缔合对过冷醇的渗透性和弛豫特性变化的影响，此处使用了两种技术：（i）在2-丙醇中引入C〜5基团以获得1-苯基-2 -丙醇，从而增加了对氢键的位阻，并且（将后者溶于2-甲基戊烷中，因此通过在非极性溶剂中分离分子而降低了氢键的程度。）过冷液体的宽带介电谱研究在188-238 K范围内对-pheny1-2-丙醇及其在2-甲基戊烷中的1：1（mol：mol）混合物进行了研究，表明根据Davidson-Cole分布，约94％的总极化衰减。在2-丙醇中取代苯基时，弛豫时间和平衡渗透率降低。介电行为的统计理论分析表明，该降低是由于取向相关系数fac的降低引起的。也可以在与2-甲基戊烷的混合物中发生这种情况。与2-丙醇相比，诱导的位阻降低了分子间H键的程度。松弛率遵循非阿累尼乌斯温度依赖性。已对Dyre理论的定性进行了定性检验，认为与经典的解释中一样，表观的阿累尼厄斯能量本身是温度依赖性的，而在合作性的定量中则定量地确定了：重新排列区域的大小，并不意味着存在一个平衡液体中潜在的热力学转变弛豫率也符合幂定律，其中l-苯基-2-丙醇的临界指数为14.52，混合物的临界指数为12.9，而不是模式耦合理论通常要求的2至4，这表明幂的歧义性。 -法律方程式。在高频下观察到的过量介电损耗可能表明纳格尔（Nagle）的“翅膀”，或者是Johari-oldstein合并弛豫。

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