Structure Determinations of Conformations by NMR

California Institute Of Technology, Pasadena CA

Investigators

Abstract

With this award the Organic and Macromolecular Chemistry Program supports the work of Dr. John D. Roberts at the California Institute of Technology in Pasadena, California. The work will build on earlier work of the PI on substituent effects on conformational equilibria of 1,2-disubstituted ethanes. These equilibria will be studied by NMR using proton-proton vicinal coupling constants, which depend on the average dihedral angle between the planes defined by the C-C bond and the bonds from these central carbon atoms to their substituents. The initial emphasis will be on repeating and reinterpreting measurements on succinic acid (HOCOCH2CH2CO2H) and its salts reported by Prof. Chidichimo at the University of Calabria. Extensions will include other solvent systems, including lyotropic media, and other molecules, such as aminoacids. The proposed research involves a fundamental question in organic chemistry: What determines the angle of rotation about carbon-carbon single bonds in organic molecules, many of which contain C-C bonds that can be regarded as 1,2-disubstituted ethanes. These angles determine the 3D structures, and many of the properties, of many organic molecules, including those involved in biological systems. In addition to shedding light on an important subject, the work is expected to provide excellent training for the postdoctoral and undergraduate students involved.