High-pressure NMR studies on solvation structure in supercritical carbon dioxide

F-19 NMR chemical shifts of 2,3,4,5,6-pentafluorotoluene, chloropentafluorobenzene, and perfluoro(methylcyclohexane) in dilute carbon dioxide solutions were precisely determined at a fixed temperature of 314.3 K over a wide range of pressure from 1 to 35 MPa. We presented an analytical procedure to determine the local solvent densities around the solutes by means of the solvent-induced chemical shifts. The local solvent densities around the different fluorines of the solutes were discussed in comparison with the previous results of hexafluorobenzene and octafluorotoluene in terms of the substitutional and aromatic ring effects. It has become apparent that the local solvent densities are quite sensitive to the molecular structures of solutes. (C) 2002 Elsevier Science B.V. All rights reserved.