Correlation Between Molecular Structure and GC Retention of Mono and Sesquiterpenic Hydrocarbons: The Influence of Shielding Steric Effects; A New Polarity Factor for Stationary Phases

Abstract

A series of mono and sesquiterpenic hydrocarbons, which differ either in the number of rings forming the molecule or in the number of double bonds located on the same carbon frame, have been studied in terms of Kováts' Δl. Two main facts have been observed: a) the existence of additional steric effects, and b) the possibility of computing Δl for mono and polycyclic compounds with up to four substituents per ring. A new tabulation for alicyclic compounds which yields superior results, obtained from Kováts' original data, is introduced. In addition, a useful classification of shielding steric effects is proposed. A better correlation is found between the experimental and computed Δl, by using the experimental 4Δl/δT for each compound instead of the temperature coefficients for each adhering zone computed after Kováts. A new relative polarity factor for stationary phases is introduced, which has a different value for each type of adhering zone.