MOLECULAR MECHANICS CALCULATIONS AND COMPARISON OF PROTON, FLUORINE, AND CARBON NMR DIASTEREOMER DISCRIMINATION VIA NONBONDING INTERACTIONSBETWEEN FLUORINE-LABELED ENANTIOMERIC AMIDES AND ENANTIOMERICALLY PURE CHIRAL SOLVATING AGENTS

Diastereomer discrimination of fluorine-labeled enantiomers in chlorof orm solutions was studied with and without two chiral solvating agents (IS and 2S) using H-1, C-13, and F-19 NMR spectroscopy. Although by C -13 NMR spectroscopy the diastereomer discrimination is not observable , changes of chemical shifts for some carbon atoms unambiguously show formation of nonbonding interactions between the enantiomers and the c hiral solvating agents. The position and the ratio of signal sets in b oth hydrogen and fluorine NMR spectra correspond to the enantiomeric c omposition in the solution. On the basis of changes in the chemical sh ifts of enantiomers in chloroform solutions of chiral solvating agent, binding constants and binding energy differences were calculated. Usi ng the MM2 force field, calculations were performed on binding complex es between the chiral solvating agent 2S and enantiomers 6. It was sho wn that demand for energy differences between diastereomeric nonbondin g complexes of racemic amides and the chiral solvating amides necessar y to obtain their NMR diastereomer discrimination is low for H-1, inte rmediary for F-19, and high for C-13 NMR.