Isomeric Effects:

(1) The figures below show the excess enthalpies (HE) and binary vapour-liquid phase diagram of the three isomeric n-hexynes (1) in n-octane (2) at T=30°C. The good correspondence between experiment and the COSMOtherm prediction is obvious. In addition, COSMOtherm is able to reproduce the qualitative differences between the hexyne isomers, which results form the chemically different environment of the triple-bond in 1-hexyne (a hydrogen atom terminating the triple bond, which can be expected to be slightly acidic) and 2- and 3-hexyne (no terminal hydrogen, thus very similar chemical behaviour). Note, that such isomeric effects can not be reproduced by group contribution methods like UNIFAC (UNIFAC predictions are also given in the Figures). Apart from COSMOtherm only thermodynamical models such as DISQUAC are applicable to this system, however to the price of having to fit experimental data of the binary system to the DISQUAC model and thus losing the generality and independence from experimental data which is a primary quality of COSMOtherm.
The COSMOtherm predictions of GE and HE are in good agreement with experiment as well as with a DISQUAC study done for the hexyne - n-octane system (compare G. Boukais-Belaribi et al. Fluid Phase Equilibria 167, 83 (2000)).

(2) The figure below show the binary vapour-liquid composition diagram and the COSMO surfaces of two isomeric nitrile-ester compounds (Exp. data providedby C. Rose, Lonza Group, CH). COSMOtherm is able to resolve the very small differences in electronic effects the isomers!

Experimental data:

(1) G. Boukais-Belaribi, B. F. Belaribi, A. Ait-Kaci and J. Jose, Fluid Phase Equilibria 167 (2000) 83-97.
(2) C. Rose, Lonza Group, CH.

COSMOtherm calculations were done using Turbomole BP-TZVP-COSMO with the standard parametrization for this method/basis set combination.