Electron spin resonance studies of reduction by solvated electrons in liquid ammonia. Part III. Aromatic carboxylic acids

Electron attachment to series of ring-substituted aromatic carboxylate mono- and di-anions in liquid ammonia solution to give e.s.r. spectra of the corresponding paramagnetic transient intermediates has been accomplished by means of the rapid-mixing cell described in Part I. Benzoic, thiobenzoic, isophthalic, and terephthalic acids and the toluic, 4-methoxy-, and dimethylbenzoic acids yield the radical-anions, ArCO2n·, but the halogen-substituted acids shed halogen to yield C6H5CO22–·, with the exception of the fluoro-acids which initially yield the substituted radical-anion (although subsequent loss of F from p-fluorobenzoic acid occurs in the course of milliseconds). Two nitrodicarboxylic acids show unusual behaviour; the species produced initially in the flow system correspond to the parent molecule plus a hydrogen atom, the presence of the extra proton in the system being marked by an additional coupling of ca. 12 Oe; these entities change rapidly to more stable radicals with spectra attributable to the ‘normal’ radical-anions. Huckel and McLachlan calculations have been carried out on all the new radicals described.