ESR studies on solvation by using s-butyl trifluoroacetyl nitroxide probe.

Stable s-butyl trifluoroacetyl nitroxide (3) has been generated in electron-transfer reaction of O-benzoyl-N-s-butylhydroxylamine (1) and trifluoroacetyl peroxide (2) in F113 (CFCl[sub 2]CF[sub 2]Cl) solution at room temperature. ESR measurement of a[sub N] and a[sub H][sup β] values for 3 in 21 solvents has been carried out at 24~ 25°C. The a[sub N] values for 3 in 12 aprotic solvents show a linear correlation with the cybotactic solvent parameters E[sub T] and Z, i.e. a[sub N] = 1.35×10-[sup 2] E[sub T]+6.84, a[sub N] = 0.78×10-[sup 2]Z+6.88. The physical significance for the slopes, slope × E[sub T] or slope × Z, the extrapolated intercepts on the a[sub N] axis are linked to the sensitivity of the nitroxide toward the solvation, the magnitude of the overall solvaton effect on the a[sub N] values, and the intrinsic a[sub N] value of 3 in the ideal gaseous state, respectively. The plots of a[sub N] versus noncybotactic solvent constants, such as dipolar moment (μ) and dielectric constant (ε), all show random cases. [ABSTRACT FROM AUTHOR]