SOLVENT EFFECTS ON FLUORINE SHIELDING IN FLUOROBENZENE

Computer simulations of fluorobenzene dissolved in ten organic liquids and water have been used to explore the origins of solvent-induced ch anges in the fluorine chemical shielding parameter when this molecule is transferred from the gas phase to a solvent. Relying on recent theo retical calculations, it is demonstrated that short-range (van der Waa ls) interactions between the fluorine nucleus and solvent molecules ar e the predominant source of shielding parameter changes. Electric fiel ds created by the solvent also have a detectable effect on shielding, The approaches used to estimate the van der Waals and electrostatic co ntributions inherently contain adjustable parameters and, if these are optimized, excellent agreement between calculated shielding effects a nd those found experimentally is obtained. The treatment used leads to reliable estimates of solvent-induced changes for solvents as diverse as water, hexane, and methylene iodide.