A simple molecular model for adsorption chromatography. VII. Relationship between the RM value and the composition for phenols in systems of the type (cyclohexane+polar solvent)/silica

Summary The effect of the composition of binary developing solvents on R_M values of phenols with one, two or three hydroxyl groups was investigated. In most cases linear R_M vs. (log X_S) relationship were obtained for wide composition ranges (X_S — mole fraction of polar solvent; diluting solvent: cyclohexane), the slope of the lines being related to the molecular mechanism of adsorption. The slopes of some derivatives of quinoline, aniline and phenols are compared and the effects of the molecular structure of the solute and the eluen strength of solvent are discussed. The experimental data for phenols are interpreted in terms of competitive solvation in the mobile phase by electron donor solvents; practical rules concerning optimization of TLC systems for the analysis of the compounds investigated are formulated.