CONFORMATIONAL STUDY BY DYNAMIC NMR SPECTROSCOPY

提议的研究涉及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。这些项目预计将提供证据，证明附着在酯的羰基上的电子释放基团会增加e -异构体的数量，而附着在酯的“醚”氧上的吸电子基团也会增加e -异构体的稳定性。要研究的化合物包括乙酸、三氟乙酸、草酸、丙酮酸、甲酸以及甲酸和乙酸的氰酸酯。RCO2 R‘中氧与R’键的旋转势垒会影响酯中E和Z构象之间的自由能差，势垒越小，熵越大，自由能越低。对甲酸叔丁酯和甲酸三苯甲酯等化合物的这些屏障进行了研究。酯类化合物广泛存在于生物系统中，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.