An effect of the nitrogen substituents in 8 is to significantly stabilize the singlet state. ![]() DFT calculations were performed on models of 8, 12, 14, 20, and on other related zwitterions 9 and 10 in order to examine the influence of the fused cycles on the charge separation and on the singlet−triplet energy gap. Furthermore, when a reaction with the electrophilic reagent results in deprotonation, as in 17− 21, there remains no charge in the system to be delocalized. When the electrophile simply adds to the zwitterion as in 12, 14, or 15, there is no more negative charge to be delocalized and only the positive charge remains delocalized between the nitrogen atoms. Dependent on the electrophile used, the control of the π system delocalization becomes possible. The acidity of the N−H protons of 8 can be modulated by an external reagent. Its reactivity with electrophiles such as H +, CH 3 +, and metal salts leads to the synthesis of new 12 π electron molecules 12 (H +), 14 (CH 3 +), and 20 (Pd 2+), respectively, in which one or both 6 π electron subsystems localize into an alternation of single and double bonds, as established by X-ray diffraction. It is shown that 8 is best described as constituted of two chemically connected but electronically not conjugated 6 π electron subunits. This molecule is a rare example of a zwitterion being more stable than its canonical forms. ![]() A straightforward synthesis of the zwitterionic benzoquinonemonoimine 8 is reported.
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