Morgado Pedro, Garcia Ana Rosa, Ilharco Laura M, Marcos João, Anastácio Martim, Martins Luís F G, Filipe Eduardo J M
Departamento de Química e Farmácia, FCT, Universidade do Algarve , Campus de Gambelas, 8000 Faro, Portugal.
Centro de Química de Évora, Escola de Ciências e Tecnologia, Universidade de Évora , Rua Romão Ramalho, 59, 7000-671 Évora, Portugal.
J Phys Chem B. 2016 Sep 29;120(38):10091-10105. doi: 10.1021/acs.jpcb.6b04297. Epub 2016 Sep 19.
This article reports a combined thermodynamic, spectroscopic, and computational study on the interactions and structure of binary mixtures of hydrogenated and fluorinated substances that simultaneously interact through strong hydrogen bonding. Four binary mixtures of hydrogenated and fluorinated alcohols have been studied, namely, (ethanol + 2,2,2-trifluoroethanol (TFE)), (ethanol + 2,2,3,3,4,4,4-heptafluoro-1-butanol), (1-butanol (BuOH) + TFE), and (BuOH + 2,2,3,3,4,4,4-heptafluoro-1-butanol). Excess molar volumes and vibrational spectra of all four binary mixtures have been measured as a function of composition at 298 K, and molecular dynamics simulations have been performed. The systems display a complex behavior when compared with mixtures of hydrogenated alcohols and mixtures of alkanes and perfluoroalkanes. The combined analysis of the results from different approaches indicates that this results from a balance between preferential hydrogen bonding between the hydrogenated and fluorinated alcohols and the unfavorable dispersion forces between the hydrogenated and fluorinated chains. As the chain length increases, the contribution of dispersion increases and overcomes the contribution of H-bonds. In terms of the liquid structure, the simulations suggest the possibility of segregation between the hydrogenated and fluorinated segments, a hypothesis corroborated by the spectroscopic results. Furthermore, a quantitative analysis of the infrared spectra reveals that the presence of fluorinated groups induces conformational changes in the hydrogenated chains from the usually preferred all-trans to more globular arrangements involving gauche conformations. Conformational rearrangements at the CCOH dihedral angle upon mixing are also disclosed by the spectra.
本文报道了一项关于氢化和氟化物质二元混合物相互作用及结构的热力学、光谱学和计算相结合的研究，这些混合物通过强氢键同时相互作用。研究了四种氢化醇与氟化醇的二元混合物，即（乙醇 + 2,2,2 - 三氟乙醇（TFE））、（乙醇 + 2,2,3,3,4,4,4 - 七氟 - 1 - 丁醇）、（1 - 丁醇（BuOH）+ TFE）和（BuOH + 2,2,3,3,4,4,4 - 七氟 - 1 - 丁醇）。在298 K下测量了所有四种二元混合物的过量摩尔体积和振动光谱，并进行了分子动力学模拟。与氢化醇混合物以及烷烃和全氟烷烃混合物相比，这些体系表现出复杂的行为。对不同方法所得结果的综合分析表明，这是由于氢化醇与氟化醇之间优先形成氢键以及氢化链与氟化链之间不利的色散力之间的平衡所致。随着链长增加，色散作用的贡献增大并超过氢键的贡献。就液体结构而言，模拟结果表明氢化链段与氟化链段之间可能存在分离，这一假设得到了光谱结果的证实。此外，对红外光谱的定量分析表明，氟化基团的存在会使氢化链的构象从通常优选的全反式转变为涉及gauche构象的更球状排列。光谱还揭示了混合时CCOH二面角处的构象重排。
