MEDIUM EFFECTS ON CONFORMATIONAL ISOMERISM

我们提出互补气相和液相核磁共振构象研究

We propose complementary gas and liquid phase NMR studies of conformational equilibria and conformational dynamics in both polar and nonpolar cyclic and acyclic molecules which model biologically important functional groups. This research is aimed at elucidating the direction and extent of solvent perturbations on torsional potential functions and conformational processes. Below we will demonstrate that for many model compounds such as amides, cyclic amines, and diazoketones it is possible with techniques we have recently developed to measure the temperature dependence of conformer populations and interconversion rates in the gas phase with NMR spectroscopy to yield a complete set of thermodynamic and kinetic parameters characterizing each conformational process. Comparison with corresponding liquid phase results will allow elucidation of the magnitude of intrinsic and environmental contributions to each internal rotation potential function. For each class of compounds, a series of molecules with systematic variations in substituent size and polarity will be investigated. Intramolecular effects on torsional potentials and conformational dynamics will be probed by comparison of gas phase thermo-dynamic and kinetic data within each series. Intermolecular effects will be probed by comparison of gas and solution data for each molecule within a series. Complementary microwave spectral data will provide additional structural and dynamic information. These studies will yield widely applicable parameters for solvent contribution to torsional potentials of biologically important functional groups and their associated conformational equilibria and dynamics. This information is essential for progress in elucidating molecular potentials, dynamics and mechanisms of conformational processes in biomolecules.