Separation of diastereoisomers by gas–liquid chromatography : esters of butane-2,3-diol

Abstract

The gas-chromatographic retention behaviour of a series of diastereoisomeric dialkyl esters of butane-2,3-diol has been investigated on a series of stationary phases varying in polarity from squalane to 1,2,3,4-tetra-(2-cyanoethoxy)-butane. The diesters were separated into meso- and racemic forms on all stationary phases, the degree of separation improving with increasing polarity of the phases. In every case, the racemic form had a higher retention volume than the meso- form. This feature may be explained in terms of the proportion of conformers existing in each case with aligned and adjacent dipoles, and the resulting stabilisation which the dipoles experience when these conformers are dissolved in a solvent. The suggested mechanism should be generally applicable to predicting the retention behaviour of isomers having polar groups on adjacent atoms provided that these groups experience a mutual electrostatic repulsion.