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We have undertaken atomistic molecular simulations to systematically determine the structural contributions to the hydrophobicity of fluorinated solutes and surfaces compared to the corresponding hydrocarbon, yielding a unified explanation for these phenomena. We have transformed a short chain alkane, n-octane, to n-perfluorooctane in stages. The free-energy changes and the entropic components calculated for each transformation stage yield considerable insight into the relevant physics. To evaluate the effect of a surface, we have also conducted contact-angle simulations of water on self-assembled monolayers of hydrocarbon and fluorocarbon thiols. Our results, which are consistent with experimental observations, indicate that the hydrophobicity of the fluorocarbon, whether the interaction with water is as solute or as surface, is due to its 'fatness.' In solution, the extra work of cavity formation to accommodate a fluorocarbon, compared to a hydrocarbon, is not offset by enhanced energetic interactions with water. The enhanced hydrophobicity of fluorinated surfaces arises because fluorocarbons pack less densely on surfaces leading to poorer van der Waals interactions with water. We find that interaction of water with a hydrophobic solute/surface is primarily a function of van der Waals interactions and is substantially independent of electrostatic interactions. This independence is primarily due to the strong tendency of water at room temperature to maintain its hydrogen bonding network structure at an interface lacking hydrophilic sites. solubility | hydration | wetting doi/ 10.1073/pnas.0915169107

Classical trajectory calculations on intramolecular vibrational energy redistribution (IVR) involving the torsion in 1,1,1-trifluoroethane (TFE) are reported. When the torsion is excited, the distortion of the C[H.sub.3] and C[F.sub.3] rotors needed to achieve the geometry of the transition state introduces increase in the energy requirement for reaction.

A direct dynamic study on the gas-phase reactions of OH radical with polyfluorinated ethanes was carried out. The main interactions between reactant and product molecules in the pre-reactive complexes are weak hydrogen bonds between hydrogen atoms from the OH radical or water, and fluorine atoms from the hydrocarbon moiety.

The positioning of an added electron in the molecular orbital of cage fluorocarbon resulting in their high electron affinities is investigated. This is verified by electronic structure calculations of all fluorinated cyclic hydrocarbons and other fluorinated cage and ring compounds.

Torsional potential energy profiles for two classes of substituted perfluoroalkanes-hydrocarbon-fluorocarbon diblocks and 1-bromoperfluorolakes-are calculated ab initio by incorporating correlation effects and using flexible basis sets. Dihedral angle functions for use in molecular simulations are derived from the quantum mechanical profiles.