Anwendung der NMR-Spektroskopie chiraler Assoziate 12: Rate determination of an intramolecular motion in a free molecule by means of dynamic NMR measurements in the presence of an auxiliary compound

Abstract

The rate constants of intramolecular processes can sometimes be measured only in the presence of optically active auxiliary compounds. The problem of obtaining the rate for the free molecule was solved by linear extrapolation of rate constant from the complexed to the uncomplexed molecule (LERCUM). This method is developed theoretically and checked experimentally. 2-Bromo-2-methyl-1-(3-bromo-2-methoxy-4,5,6-trimethylphenyl)-1-propanone has the advantage that rotation about its carhonyl-to-aryl bond can be measured both in the presence of (+)−2,2,2-trifluoro-1-phenylethanol as well as in the absence of an auxiliary compound. The novel method of extrapolation is confirmed by the agreement between both results.