Studies of estimation procedures for physico-chemical properties of small molecules in the liquid phase

Abstract

This study examines estimation procedures for physico-chemical properties of small molecules in the liquid phase. Both strongly and weakly interacting systems are considered. The halogenated methanes were chosen for the investigation since they represent a large subclass (70 species) of relatively simple, rigid and strongly interacting molecules. The bond, geminal and trigonal additivity procedures were studied as estimation procedures for three different physical properties: carbon-13 NMR chemical shifts, density or molar volume, and molar refractivity and 20°C. In general, it was found that the best correlations were achieved using the trigonal procedures while the bond procedure gave the least satisfactory results. In order to expand the data base for the halomethane carbon-13 chemical shifts, procedures were developed for the synthesis of various chlorine and iodine-containing and bromine and iodine-containing halomethanes and the carbon-13 shifts of these compounds were measured. Techniques were also developed for the estimation of trigonal additivity parameters which were not experimentally available. The chemical shifts of all 70 halomethanes could be correlated using the bond, geminal, and trigonal additivity techniques. Both the geminal and trigonal procedures yielded correlations which were superior to those of previously published techniques for this class of compounds. The standard deviation of the trigonal technique was within experimental uncertainties. Sufficient literature data was available for the correlation of the molar volumes (at 20°C) of all seventy halomethanes using the bond additivity technique, 55 halomethanes using the geminal technique and 48 halomethanes using the trigonal technique. It was found that the trigonal additivity technique was required to obtain completely satisfactory correlations. As might be expected from the results of previous workers, all three additivity techniques yielded acceptable correlations of molar refractivity. The bond correlation were improved by using the geminal and trigonal techniques...