Lack of delocalization in compounds with the grouping CNNC

Whereas for molecules containing the grouping XCCY (X, Y=C, O, N, S) delocalization of electrons is well established, it is concluded here that in both cyclic and acyclic compounds containing the grouping CNNZ (Z=C, N) the delocalization is either minimal or absent. Electrochemically determined reduction potentials are a useful tool for estimating the extent of conjugation.