The (19)F spectra with natural-abundance carbon-13 satellites of C(6)F(5)X (X = H, Cl or I) in ZLI 1695 liquid crystal were analysed. Excluding fluorine-fluorine dipolar coupling constants from the fitting, the vibrationally corrected structures of these molecules were derived and compared with those calculated at DFT/B3LYP level of theory with the aug-cc-pVTZ basis set. The results show that pentafluorobenzene did not exhibit noticeable distortion of the aromatic ring, while chloropentafluorobenzene and iodopentafluorobenzene molecules showed some deformations in their determined structures. Relative anisotropies of F-F couplings have been deduced with accuracy for C(6)F(5)H molecule. Due to uncertainties in structure determination of C(6)F(5)Cl and C(6)F(5)I molecules, it was not possible to obtain precise values for all the corresponding anisotropies. In addition, it was found that the orientation of these molecules in the solvent used can be qualitatively explained in terms of dispersion forces.
The gas phase proton affinities PA and basicities GB for a series of para-substituted acetophenones weak bases (B) p.X-C(6)H(4)CO*CH(3) with X=H, F, Cl, Br, I, Me, CF(3), CN, NO(2), OCH(3), NH(2), CH(2)OH, N(CH(3))(2), OH, [Formula: see text], … have been calculated at 298.15 K at the density functional theory DFT/B3LYP level with a 6-311++G (2d,2p) basis set. Conformational results lead to only one stable planar conformer for both unprotonated compounds and their O*-protonated forms. Satisfactory accuracy and computational efficiency could be reached if the computed PAs are scaled by a factor 0.983. Protonation at more than one site is discussed and the carbonyl oxygen atom is found to be the preferential protonated site rather than the substituent X. The calculated gas phase PAs show a good agreement with the experimental available data. The electron-donating/electron-withdrawing nature of the substituents has an enormous influence upon the thermochemical and structural properties. The influence of environment on the proton affinity has been studied by means of SCRF solvent effect computations using PCM solvation model for two solvents: water and SO(2)CI(2). Confrontation between computed and experimental pK(B) values exhibits better agreement in aqueous solution than in organic solvent.
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