Planar compounds trioxide

The existence of the fugitive, paramagnetic trioxide NO3 is also implicated in the N2O5-catalyzed decomposition of ozone, and its concentration is sufficiently high for its absorption spectrum to be recorded. It has not been isolated as a pure compound, but probably has a symmetrical planar structure like that of NOJ. 

Sulfur trioxide (SO3) is an industrially important compound key to the production of sulfuric acid. It tends to polymeric forms both in the solid and liquid states. As a gas, the molecules have a planar triangular structure in which the sulfur atom has a high affinity for electrons. This explains its action as a strong Lewis acid towards bases that it does not oxidize. It can thus crystallize complexes with pyridine or trimethy-lamine. It has a very strong affinity for water and hence rapidly associates with water in the environment. 

In the series [18]annulene trisulphide, oxide-disulphide, dioxide-sulphide and trioxide, the relationship between planarity and delocalization has again been demonstrated. The trisulphide and oxide-disulphide are predicted from Catalin models to be non-planar and their n.m.r. does reflect the absence of a ring current over the total 18 -re-electron system. Models suggest that the dioxide-sulphide is near-planar and the trioxide planar, and indeed these compounds are aromatic 183,185)... 

The structure of nitric acid is retained in the crystalline phase. The anhydride, however, crystallizes as an ionic compound, nitryl nitrate or (N02)+(N03) . The nitryl cation, which is isoelectronic with carbon dioxide, is linear. The nitrate ion which, is valence shell isoelectronic with sulfur trioxide, is trigonal planar. 

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