Activity Coefficients

The article Prediction of Infinite Dilution Activity Coefficients of Organic Compounds in Aqueous Solution from Molecular Structure (Mitchell, J. Chem. Inf. Comput. Sci. 1998, 38, 200-209) describes a QSPR method for predicting activity coefficients. The authors achieved rather good results, with a standard deviation of 0.35 ln units. The same calculations were performed using COSMOtherm. Both series of results are shown in the graph below:

Many of the compounds were either gases or solids, and therefore did not yield results as good as for the liquids. 240 of the compounds were liquids, and lead to a standard deviation of 0.77 ln units. Among the outliers, only two of them showed an error above 2 ln units. In this particular study, it is not clear when studying the outliers why these particular compounds led to poorer results, since most of them have the same functional groups as the compounds for which the results were very close to the experimental value.

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