Origins of the solvent chain-length dependence of Gibbs free energies of transfer

Experimentally measured partition coefficients show that the solubilities o f small solutes in normal alkanes depend on the solvent chain length (n(C)) . The causes for this ne dependence have not yet been unambiguously determi ned, and there is considerable controversy as to whether different interact ions with methyl and methylene groups or entropic Flory-Huggins-like effect s might play the major role. We have performed Gibbs-ensemble Monte Carlo s imulations to study the vapor-liquid partitioning of methane in normal alka nes (with 6-12 carbon atoms) and related model solvents. The simulations sh ow that the increase in solvent density with increasing n(C) is the main or igin of the ne dependence for normal alkanes; that is, the solute molecule feels a different environment depending on the alkane chain length.