Dynamic interconversion of chiral oxime compounds in gas chromatography

A number of chiral oxime compounds have been synthesised and their gas chromatographic analysis on both a polyethelene glycol phase column and two chiral column phases was investigated. Of particular interest to this work is the observation of dynamic interconversion behaviour, both in a single dimensional analysis, and by using comprehensive two-dimensional gas chromatography (GC × GC). A number of non-chiral compounds were studied as a means to understand the nature of the behaviour observed. As expected, the achiral compound on both the wax column and the chiral column generated two isomeric compounds—the E and Z isomers. On the wax column, a characteristic interconversion zone representing the dynamic process was observed, with extent of interconversion dependent on the conditions used. For the chiral compounds, two isomers and the interconversion zone were exhibited on the wax column, however on the chiral column 4 isomeric peaks were found—the (R) and (S) enantiomers of each of the E and Z isomers. In the case of the chiral column, the extent of interconversion was negligible, and this appears to correlate with the use of low polarity columns. In order to encourage dynamic interconversion, a polyethylene glycol column was coupled to the chiral column, by placing it either before or after the chiral column. In this case a monitor detector was employed between the two columns in order to isolate the effects of the first column from the behaviour on the second. In a further study, the most appropriate column arrangement from the earlier study was placed into a comprehensive two-dimensional gas chromatography instrument, with a wax-phase column in the second dimension. The unique location of peaks for each of the molecules in 2D space and patterns for the interconversion processes is interpreted phenomenologically.