CONFORMATIONAL STUDY BY DYNAMIC NMR SPECTROSCOPY

建议的研究包括应用动态核磁共振波谱和/或计算方法来研究一系列羧酸、酯和相关化合物的构象平衡。这些项目有望提供证据，证明附着在酯基上的电子释放基团将增加E-异构体的数量，而附着在酯的“乙醚”氧上的吸电子基团也将增加E-异构体的稳定性。要研究的化合物包括醋酸、三氟乙酸、草酸、丙酮酸、甲酸和乙酸氰酸酯。在RCO2R‘中，氧与R’键之间的转动势垒会影响酯类中E和Z构象之间的自由能差，势垒越小，自由能越高，自由能越低。对包括甲酸叔丁酯和甲酸三苯甲酯在内的几种化合物中的这些势垒进行了研究。酯类化合物广泛存在于生物体系中，其性质受其构象的影响。

The proposed research involves the application of dynamic NMR spectroscopy and/or computational methods to studies of the conformational equilibria of a series of carboxylic acids, esters, and related compounds. The projects are expected to provide evidence that electron-releasing groups attached to the carbonyl group of an ester will increase the population of the E-isomers, and electron-withdrawing groups attached to the "ether" oxygen of an ester will also increase the stability of the E-isomers. Compounds to be studied include acetic acid, trifluoroacetic acid, oxalic, pyruvic acid, performic acid, and the cyanate esters of formic acid and acetic acid. Rotational barriers about the bond between oxygen and R' in RCO2 R' should affect the free-energy difference between E and Z conformations in esters, which a smaller barrier giving rise to a higher entropy and lower free energy. Studies of these barriers in several compounds, including tert-butyl formate and triphenylmethyl formate, are proposed. Esters occur widely in biological systems, and their properties are influenced by their conformations.