Multistep Reversible Redox Systems, XLVII1)N,N′‐Dicyanoquinonediimines – A New Class of Compounds, II: Comparison of Redox Properties with those of Quinones and Tetracyanoquinodimethanes

Abstract

By determining the E₂ (and in part E₁) redox potentials of the quinoid compounds 1–9, the close chemical similarity of the groups C = X [X  O, NCN, C(CN)₂] has been quantitatively confirmed. Especially the dicyanodiimines 2 and 5 are very similar to TCNQ derivatives 3. Substituent effects on the potentials E₂ are linear with (σ_m + σ_p)/2 Hammett constants. Most deviations from the expected thermodynamic stability of the radical anions (K_SEM) are due to lack of planarity especially with systems containing the Y‐shaped rigid =C(CN)₂ group.