Submitted to: American Chemical Society National Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 15, 1999
Publication Date: N/A
Technical Abstract: Metolachlor exists as a racemic mixture of two sets of enantiomers aS,12S (aR,12R) and aR,12S (aS,12R) and multiple stable conformatons. NMR and molecular and quantum mechanics were used to determine the different conformations of metolachlor isomers in solution. The minimum energy conformations, in the gas phase, were determined by varying the dihedral angles and energy minimization to find a local minimum on the potential energy surface of each new structure. One-Dimensional Nuclear Overhauser Enhancement Difference Spectra (NOEDS) and 2D Nuclear Overhauser Enhancement Spectroscopy (NOESY) revealed that one stable conformation in each set of metolachlor enantiomers was favored in a solvent medium. 1H- and 13C-NMR experiments in different chemical environments identified the labile sites of metolachlor most susceptible to conformational changes and the identify chemical environments that induce such changes. Within very specific chemical environments, metolachlor atropisomers aS,12S (aR,12R) and aR,12S (aS,12R) freely interchange and consequently the multiple conformations also interchange. The changes which most alter the conformations and molecular dynamics of metolachlor may enable identifying the critical components in chemical environments that most affecting its environmental fate. These results make possible a structural interpretation of conformational changes on binding to environmental substrates.