4n pi electrons but stable: N,N-dihydrodiazapentacenes.

Despite having 4n pi electrons, dihydrodiazapentacenes are more viable than their 4n+2 pi azapentacene counterparts. Ab inito valence bond block-localized wave function (BLW) computations reveal that despite having 4n pi electrons, dihydrodiazapentacenes are stabilized and benefit substantially from four dihydropyrazine ethenamine (enamine) conjugations. Almost all of these dihydrodiazapentacenes have large negative overall nucleus independent chemical shifts NICS(0)(pizz) values even though their dihydropyrazine rings (e.g., for 6-H(2)) are modestly antiaromatic, as their paratropic contributions are attenuated by delocalization throughout the system.