Selection of molecular descriptors used in quantitative structure gas chromatographic retention relationships .2. Isoalkanes and alkenes

Quantitative structure-retention relationships are used to relate the chromatographic retention of analytes to their molecular structure features. With well selected descriptors quick a priori prediction can be accomplished. The descriptors were distinguished in this study in four groups, namely substantial, important, likely and specific, based on their individual correlation with the gas chromatographic retention of 38 isoalkanes and 24-alkenes on different stationary phases including charcoal. No descriptor, neither from the substantial group, nor from the other groups was able to give a satisfactory fitness between calculated and experimental retention indices. A two moiety mathematical model is used to generate equations and owing to the goodness of the fit of some of the equations, several pairs of substantial/specific descriptors were selected as most suitable for prediction purposes. To increase the accuracy in prediction in adsorption mode chromatography, the quantum chemical calculations of descriptor values is proposed to be made for all possible conformation states.