Electron spin resonance studies of solvation.
thesisposted on 19.11.2015, 08:46 by J. Oakes
This thesis presents an electron spin resonance study of solvation as revealed by environmental modifications of the three related semiquinones, p-benzosemiquinone, duro-semiquinone and 2, 6-dimethyl-p-benzosemiquinone and the p-dinitrobenzene anion. Brief reviews are given of the numerous processes which Can give rise to line-broadening. It is shown how a knowledge of these factors is of considerable utility to the experimental and theoretical chemist. Protonation of 2, 6-dimethyl-p-benzosemiquinone is shown to occur at the unhindered oxygen atom. Previous assignments of the coupling constants of monoprotonated semiquinones are confirmed. A correlation of the proton hyperfine splitting constants with the Z-value of the solvent is described. The various degrees of line-broadening associated with the e.s.r. spectra of ion-pairs of semiquinones in a range of solvents is attributed to transfer of the cation from one oxygen atom of the semiquinone to the other. The e.s.r. spectra of a range of ion-pairs of 2, 6-dimethyl-p-benzosemi-quinone in t-pentanol and 1, 2-dimethoxyethane show that the cation favours the oxygen atom remote from the methyl groups. Variation in the magnitude of the sodium hyperfine coupling constant of the sodium salt of 2, 6-dimethyl-p-benzosemiquinone is reported and is interpreted in terms of intramolecular interconversion between isomeric ion-pairs as also is the disproportionate broadening of the outer lines of the sodium quartet. It is shown that the concentration ratio of these ion-pairs is about 9 : 1 in favour of an association at the oxygen atom remote from the methyl groups. The proton hyperfine splitting constants of 2, 6-dimethyl-p-benzosemiquinone have been found to be solvent dependent. Possible correlations between these parameters and solvent characteristics are discussed. The dependence of the 14N coupling constant of the p-dinitrobenzene anion upon the concentration of added salt is reported. The results indicate that ion-pairing is possible in solvents such as alcohols. Several mixed solvent graphs are reported and discussed.