Studies on the reactivities of radical anions of norbornadiene and quadricyclane derivatives by pulse radiolysis

Chemical reactivities of radical anions of dimethylbicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate(NE) and dimetyltetracyclo[3.2.0.0sup(2,7).0sup(4,6)]heptane-1,5-dicarboxylate(QE) have been investigated by pulse radiolysis of hexamethylphosphorictriamide(HMPA) solutions and 77 K γ irradiation of 2-methyltetrahydrofuran(MTHF) solutions. Solvated electrons were captured by QE in HMPA with a rate constant of 1.3 x 109 dm3.mol-1.s-1 at room temperature. The resultant radical anion of QE, which could not be detected, isomerized to NE radical anion very rapidly, even at 77 K. On the other hand, the NE radical anion which was formed from NE and solvated electron with a diffusion-controlled rate, did not isomerize to QE radical anion but reacted with a neutral NE molecule with a rate constant of 1.2 x 107 dm3.mol-1.s-1. The dimer anion thus formed shows a strong UV absorption band at wavelengths shorter than 330 nm and was estimated to be a σ-bonded dimer. For the γ radiolysis of HMPA solution of NE, it has been observed that G(-NE) depends on the concentration of NE and reached 142 at 0.04 mol.dm-3 of NE, suggesting a chain reaction to form polymeric products. (author)