ESR-Untersuchung der behinderten Rotation der Acetyl-Gruppe in einigen para-X-Acetophenon-Anionradikalen

Abstract

The anion radicals of para-X-acetophenone (X = NO2 , CH3 , H, Br, OCH3) were generated by electrolytic reduction in N,N-dimethylformamide solution. The temperature dependence of the ESR spectrum of para-nitroacetophenone(-) indicates restricted rotation of the acetyl group relative to the rest of the molecule. A complete line-shape analysis of the spectrum at various temperatures leads to Arrhenius-parameters Ea= (8.9 ± 0.5) kcal/mol and 10log k0=12.7±0.3. The other radical anions show magnetic nonequivalence of their meta protons up to the highest temperature at which the spectra were observable. This enables us to set a lower limit to their potential barriers of about 11 . . . 12 kcal/mol, depending on the para substituent.