Multistep Reversible Redox Systems, XLVII 1) N,N ′‐Dicyanoquinonediimines – A New Class of Compounds, II: Comparison of Redox Properties with those of Quinones and Tetracyanoquinodimethanes

By determining the E 2 (and in part E 1 ) redox potentials of the quinoid compounds 1 – 9 , the close chemical similarity of the groups C = X [X O, NCN, 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 E 2 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.