CONFORMATIONAL STUDY BY DYNAMIC NMR SPECTROSCOPY

拟议的研究涉及应用动态NMR光谱和/或计算方法的一系列羧酸，酯和相关化合物的构象平衡的研究。预计这些项目将提供证据，证明与酯的羰基相连的释电子基团将增加E-异构体的数量，而与酯的“醚”氧相连的吸电子基团也将增加E-异构体的稳定性。待研究的化合物包括乙酸、三氟乙酸、草酸、草酸、过甲酸以及甲酸和乙酸的氰酸酯。RCO 2 R'中氧与R'键的转动势垒影响酯中E和Z构象的自由能差，势垒越小，熵越高，自由能越低。这些障碍在几种化合物，包括叔丁基甲酸酯和三苯基甲基甲酸酯的研究，提出。酯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.