Intramolecular electron exchange with solvent participation: electron spin resonance study of the radical-anion of benzene-1,3-dicarbaldehyde in propan-2-ol–water mixtures

Abstract

The short-lived radical anion of benzene-1,3-dicarbaldehyde was generated by in situ photolysis of the parent compound in pure ethanol, propan-2-ol, and propan-2-ol–water mixtures at pH >7 and identified by e.s.r. In one of the three detected rotamers (Z,E) an alternating linewidth effect was observed at temperatures between 252 and 315 K. This phenomenon was studied in terms of a two-jump model involving two asymmetrically solvated radical anions. Rates of interconversion between these two in propan-2-ol were found to be in the range 0.5–1.25 × 10⁹ s^–1. Variation of the water content in mixtures of propan-2-ol and water mainly affects the coupling consants. The 3-formyl-α-hydroxybenzyl radical (the conjugate acid of the radical anion) has also been generated by photolysis of benzene-1,3-dicarbaldehyde in pure propan-2-ol at pH 4–7 and has been studied by e.s.r.