乙酸在气相中的二聚化——核磁共振实验和量子化学计算,Molecules

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乙酸在气相中的二聚化——核磁共振实验和量子化学计算
Molecules ( IF 4.2 ) Pub Date : 2020-05-04 , DOI: 10.3390/molecules25092150
Ondřej Socha _{1,

2} , Martin Dračínský ₁

Affiliation

由于羧基的性质，乙酸可以作为氢键的供体和受体。已知气态乙酸形成具有两个强氢键的环状二聚体。然而，三聚体和各种低聚体结构也被假设存在于乙酸的气相和液相中。在这项工作中，结合气相核磁共振实验和先进的计算方法来验证气态乙酸的基本二聚模型。在玻璃管中进行的气相实验揭示了醋酸与玻璃表面的相互作用。另一方面，为聚合物插入物中的乙酸获得的可变温度和可变压力 NMR 参数提供的热力学参数与 MP2（二阶 Møller-Plesset 扰动理论）和 CCSD(T)（具有单、双和微扰三重激发）基于基本二聚化模型的计算。理论二聚模型与实验数据之间的微小差异仅在低温下显示。这一观察结果可能表明在低温下存在其他熵不利的超分子结构。理论二聚模型与实验数据之间的微小差异仅在低温下显示。这一观察结果可能表明在低温下存在其他熵不利的超分子结构。理论二聚模型与实验数据之间的轻微差异仅在低温下显示。这一观察结果可能表明在低温下存在其他熵不利的超分子结构。

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Dimerization of Acetic Acid in the Gas Phase—NMR Experiments and Quantum-Chemical Calculations

Due to the nature of the carboxylic group, acetic acid can serve as both a donor and acceptor of a hydrogen bond. Gaseous acetic acid is known to form cyclic dimers with two strong hydrogen bonds. However, trimeric and various oligomeric structures have also been hypothesized to exist in both the gas and liquid phases of acetic acid. In this work, a combination of gas-phase NMR experiments and advanced computational approaches were employed in order to validate the basic dimerization model of gaseous acetic acid. The gas-phase experiments performed in a glass tube revealed interactions of acetic acid with the glass surface. On the other hand, variable-temperature and variable-pressure NMR parameters obtained for acetic acid in a polymer insert provided thermodynamic parameters that were in excellent agreement with the MP2 (the second order Møller–Plesset perturbation theory) and CCSD(T) (coupled cluster with single, double and perturbative triple excitation) calculations based on the basic dimerization model. A slight disparity between the theoretical dimerization model and the experimental data was revealed only at low temperatures. This observation might indicate the presence of other, entropically disfavored, supramolecular structures at low temperatures.

更新日期：2020-05-04

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