The existence of peripheral ring currents in the dianion and the tetraanion of (1) is manifested in the NMR spectra. In the case of (1), the dianion, and the tetraanion, H-3 (outer) absorbs at δ = 7.37, 9.26, and 4.48, respectively, and H-4 (inner) at 7.37, −7.07 (!), and 12.76, respectively. From the viewpoint of bonding theory, it is particularly surprising that perimeter conjugation extends beyond the benzene units.
If you can't find a tool you're looking for, please click the link at the top of the page to "Go to old article view". Alternatively, view our Knowledge Base articles for additional help. Your feedback is important to us, so please let us know if you have comments or ideas for improvement.