Electrochemical properties and radical anions of carbocycle‐fluorinated quinoxalines and their substituted derivatives

Electrochemical reduction (ECR) and oxidation (ECO) of 5,6,7,8‐tetrafluoroquinoxaline (1) and its derivatives bearing various substituents R (7‐H (2), 7,8‐H2 (3), 6‐CF3 (4), 6‐Cl (5), 5,7‐Cl2 (6), 5‐NH2 (7), 6‐OCH3 (8), 6,7‐(OCH3)2 (9), 6,7,8‐(OCH3)3 (10), 5,6,7,8‐(OCH3)4 (11), 6‐OCH3,7‐N(CH3)2 (12), 6‐N(CH3)2 (13), 6,7‐(N(CH3)2)2 (14), 5,6,7‐(N(CH3)2)3 (15), and 7,8‐cyclo‐(=CF‐CF = CF‐CF=) (16)) in the carbocycle have been studied by cyclic voltammetry in MeCN. For 1–4 and 7–15, the first reduction peaks have been found to be 1‐electron and reversible, thus corresponding to the formation of their radical anions (RAs), which are long lived at 295 K except those of 4–6 and 15, 16. Irreversible hydrodechlorination has been observed for 5 and 6 at the first step of their ECR confirmed by EPR detection of corresponding RAs of 2 and 5,7‐H2 derivative of 1 (17) at the next steps. Electrochemically generated RAs of 1–3, 7–14, and 17 have been characterized in MeCN by EPR spectroscopy together with DFT calculations at the (U)B3LYP/6‐31 + G(d) level of theory using PCM to describe the solvent. A noticeable alternation of spin density on the –NCCN– moiety of quinoxaline has been observed for all RAs possessing R‐substitution asymmetry. The comparative electron‐accepting ability of 1–15 has been analyzed in terms of their experimental reduction peak potentials and the (U)B3LYP/6‐31 + G(d)‐calculated gas‐phase first adiabatic electron affinities (EAs). The differences in electron transfer solvation energies for 1–15 have been evaluated on the basis of ECR peaks' potentials and calculated gas‐phase EAs. The ECO of 1–5 and 7–14 has been found to be irreversible.