Reversible dimerization of the anion radicals of some dicyanonaphthalenes

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 2011-09, Vol.660 (1), p.91-96
• Main Authors: Astudillo Sánchez, Pablo D., Evans, Dennis H.
• Format: Article
• Language: English
• Subjects: Anion radical; Chemistry; Cyclic voltammetry; Dimerization; Electrochemistry; energy; Exact sciences and technology; free radicals; General and physical chemistry; isomers; Kinetics and mechanism of reactions; Spin density; temperature
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/j.jelechem.2011.06.010

► Study of seven isomers of dicyanonaphthalene reveals two new cases of reversible dimerization. ► Weak dimerization can be detected from the shape of the voltammogram. ► Systems with larger dimerization equilibrium constants show a separate oxidation peak for the σ-dimer. ► Dimerization equilibrium constants correlate with spin density at the site of dimerization. The electrochemical reduction of 7 of the 10 isomeric dicyanonaphthalenes has been studied in N,N-dimethylformamide. The studied compounds were 1,2-, 1,3-, 1,4-, 2,3-, 1,8-, 2,6- and 2,7-dicyanonaphthalene. For most of the isomers, the one-electron reduction to the anion radical occurred as a simple, reversible reduction without complications from coupled chemical reactions. However, for 1,3-, 2,3- and 2,7-dicyanonaphthalene, the reduction was affected by a reversible dimerization of the anion radicals. Dimerization equilibrium constants were determined at various temperatures. DFT calculations of the anion radicals of all 10 isomers provided spin densities at ring carbons 1–8. The highest spin density for carbons 1–8 not bearing a cyano group was largest for the three isomers with detectable dimerization. Not only do these calculations suggest the site of dimerization, it was found that the free energy change for dimerization varies in an approximately linear fashion with spin density.