A zwitterionic Meisenheimer complex of 2,4,6-trinitrobenzene

In molecules of the zwitterionic Meisenheimer complex 4-(N-pyridiniomethyl) -1,3-dioxolane-2-spiro-1'-2',4',6-trinitrocyclohexadienide (C14H12N4O8), th e nitro groups do not possess equivalent geometries. The C-N bond to the ni tro group pam to the saturated C atom is shorter than those of the others, and bond lengths vary considerably between the two unsaturated sections of the six-membered ring. These observations indicate a significant contributi on from a resonance form in which the six-membered ring has a 2,5-diene geo metry and the para nitro adopts the aci resonance form.