Thermodynamic, spectroscopic, and density functional theory studies of allyl aryl and prop-1-enyl aryl ethers. Part 1. Thermodynamic data of isomerization
作者:Esko Taskinen
DOI:10.1039/b101837j
日期:——
A chemical equilibration study of the relative thermodynamic stabilities of seventy isomeric allyl aryl ethers (a) and (Z)-prop-1-enyl aryl ethers (b) in DMSO solution has been carried out. From the variation of the equilibrium constant with temperature the Gibbs energies, enthalpies, and entropies of isomerization at 298.15 K have been evaluated. Because of their low enthalpies, the (Z)-prop-1-enyl aryl ethers are strongly favored at equilibrium, the Gibbs energies of the a→b isomerization ranging from −12 to −23 kJ mol−1. The entropy contribution is negligible in most reactions, but occasionally small positive values less than +10 J K−1 mol−1 of the entropy of isomerization are found. The equilibration studies were also extended to involve two pairs of related isomeric ethers with a Me substituent on C(2) of the olefinic bond. The Me substituent was
found to increase the relative thermodynamic stability of the allylic ethers by ca. 3.4 kJ mol−1.
通过对70对异构化的烯丙基苯基醚(a)和(Z)-丙-1-烯基苯基醚(b)在DMSO溶液中的化学平衡研究,考察了它们相对热力学稳定性的变化。从平衡常数随温度的变化中,评估了在298.15 K下的异构化吉布斯自由能、焓和熵。由于其低焓值,(Z)-丙-1-烯基苯基醚在平衡状态下具有显著优势,a→b异构化的吉布斯自由能范围从-12至-23 kJ/mol。在大多数反应中,熵的贡献可以忽略不计,但偶尔会发现小于+10 J/K·mol的正值。平衡研究还扩展到涉及两对在烯键C(2)位置带有甲基取代基的相关异构化醚。甲基取代基可以增加烯丙基醚的相对热力学稳定性约3.4 kJ/mol。