Browsing by Author "Wells, Cecil F."

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Ionic Solvation in Methanol+Water Mixtures: Free Energies of Transfer from Water
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (5), 1973) Wells, Cecil F.
The free energy of transfer ΔG°t(H+) of the solvated proton from water to methanol + water mixtures up to 50 % w/w methanol is considered as the sum of two processes, the transfer of a tetrahedral aqua-proton from water into the mixture using the Born expression and the subsequent replacement of an H2O molecule in the tetrahedron by a methanol molecule according to the equilibrium, H+(H2O)4solv+ CH3OHsolv⇌ H+(CH3OH)(H2O)3solv+ water. These values for ΔG°t(H+) are subsequently used to derive values for ΔG°t(halide ion) from the ΔG°t for the appropriate hydrogen halides, and ΔG°t(Cl–) then used to produce values of ΔG°t for other cations from ΔG°t for simple salts. These values for ΔG°t for the single ions are discussed with respect to solvation of ions by H2O and CH3OH molecules and structural effects in the bulk solvent.
Ionic Solvation in Water-FCo-solvent Mixtures Part 6.—Free Energies of Transfer of Single Ions from Water into Water + Dioxan Mixtures
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (06), 1978) Wells, Cecil F.
The method used earlier to calculate the free energy of transfer of the proton from water into aqueous mixtures, ΔG0t(H+), and thereby to separate ΔG0t(HX) to produce ΔG0t(X–), has now been applied to water + dioxan mixtures. Values of ΔG0t(X–) are then used to produce values for ΔG0t(M+) and ΔG0t(M2+) from ΔG0t(MX) and ΔG0t(MX2). To determine ΔG0t(H+), values for Kc=[(dioxan, H+)solv]/[H+solv][(dioxan)solv] are measured using the previously described spectrophotometric technique. All values for ΔG0t(M+) and ΔG0t(M2+) are negative in water-rich conditions; values for ΔG0t(X–) for most X– are positive, increasing with increasing [dioxan]. Contrary to the results obtained with water + alcohol mixtures where alkoxide ions are produced from added OH–, ΔG0t(OH–) in water + dioxan is in the place expected in the order of X– on structure breaking and forming properties alone. The change in the proton affinity of conjugate bases is computed for the transfer of a range of acid + base systems from water into water + dioxan; this is used to separate ΔG0t for the ion into “non-electronic” and “electronic” components. The variation of the latter with solvent composition suggests that dielectric effects of the solvent make only minor contributions compared with the structural effects.
Ionic Solvation in Water4-Co-solvent Mixtures Part 5: Free Energies of Transfer of Large Single Ions from Water into Water + Methanol with the “ Neutral ” Component Removed
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (3), 1978) Wells, Cecil F.
Values for the change in proton affinity, ΔPa, of large molecules on transferring them from water into mixtures of water with methanol have been calculated. –ΔPa for anions and ΔPa for cations represent an elimination of the non-electrostatic or “neutral” component from the free energy of transfer of the ion i, ΔG°t(i). Although plots of –ΔPa against reciprocal of dielectric constant are linear for the anions, the values of their slopes show that there is a structural component of this “electrostatic” free energy, ΔG°t(i)e, in addition to the Born contribution. ΔG°t(F–) is calculated from data newly available, and ΔG°t(halide) values are compared with ΔG°t(i)e values for the large ions. The negative values for ΔG°t(i)e for large cations confirm that there is a contribution from structural changes in the solvent; these are compared with the negative values for ΔG°t(i) for small cations.