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.
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