HYDROGEN-BONDING .21. SOLVATION PARAMETERS FOR ALKYLAROMATIC HYDROCARBONS FROM GAS-LIQUID-CHROMATOGRAPHIC DATA

The truncated solvation equation log SP = c + rR2 + l log L16 has been applied to numerous sets of gas-liquid chromatographic (GLC) data for alkylaromatic hydrocarbons on non-polar stationary phases. Here SP can be V(G) or can be the relative retention time, and the retention index I can in this context be used in place of log SP. R2 is the solute excess molar refraction, easily obtained from refractive index. A set of solutes of known log L16 is used to set up the equation and then values of log L16 can be back-calculated for other solutes; L16 is originally defined as the solute gas-liquid partition coefficient on hexadecane at 25-degrees-C. Through the above equation log L16 values were calculated for 190 solutes. Once log L16 is known, the reduced equation log SP = c + s-pi(2)H + l log L16 can be applied to GLC data on polar stationary phases, and the dipolarity/polarizability parameter pi(2)H obtained by back-calculation in a similar way. Values of pi(2)H for 120 solutes are listed. It is shown that n-alkyl substituents affect the pi(2)H value only slightly, but ortho substituents considerably increase pi(2)H, e.g., benzene (0.52), toluene (0.52), o-xylene (0.56), 1,2,3-trimethylbenzene (0.61), 1,2,3,4-tetramethylbenzene (0.65), pentamethylbenzene (0.66), hexamethylbenzene (0.72).