The push-pull substitution of 8 allows a description of their ground-state electronic structure by the resonance 8A<—+ 8B. The high contribution of 8B is documented in the 1H-NMR spectra, where the NCH3 peak appears at values (6= 3.27-3.42, except for 8a, j) that are typical for dimethylamino-cyclopropenylium ions such as 1, 5, and 6.19 Moreover, the carbonyl absorptions in the IR spectrum of acylated triafulvenes 8c—h, i—m are at ...
