Ozonides zwitterionic complexes

NMR spectroscopy, 173-8 thermal analysis, 730 X-ray crystallography, 711-12, 726-30 thermochemistry, 165-6 1,2,4-tiioxane synthesis, 290-1 zwitterionic complexes, 734 see also Final ozonides Primary ozonides Ozonization... 

Ozonation ofAlkenes. The most common ozone reaction involves the cleavage of olefinic carbon—carbon double bonds. Electrophilic attack by ozone on carbon—carbon double bonds is concerted and stereospecific (54). The modified three-step Criegee mechanism involves a 1,3-dipolar cycloaddition of ozone to an olefinic double bond via a transitory TT-complex (3) to form an initial unstable ozonide, a 1,2,3-trioxolane or molozonide (4), where R is hydrogen or alkyl. The molozonide rearranges via a 1,3-cycloreversion to a carbonyl fragment (5) and a peroxidic dipolar ion or zwitterion (6). 

While both the primary and secondary ozonides have been isolated and characterized, the pair formed by the carbonyl oxide (CO) and the carbonyl compound (CC) has never been directly put into evidence. This elusive intermediate, called also Criegee intermediate zwitterion (CZ), according to this AMI study which did not take into account solvent effects, forms a tight pair or a dipolar complex (DC). The primary ozonide has an O-envelope halfchair conformation and as such two conformers are possible from a rfr-alkene 11 and 12 and only one 13 from the trans-alkene. The splitting of the primary ozonide can lead either to an anti 14 or syn 15 CO and has a determining role for the stereochemical outcome of the reaction <1997JOC2757>. 

As mentioned in section 20.2.3, natural rubber (in common with other diene elastomers) is readily attacked by ozone. The mechanism of the reaction is probably the same as that established for simple olefins [10]. In this case, the initial product is a -complex which cleaves to form an aldehyde or ketone and a zwitterion. Several subsequent reactions may then occur, depending on the nature of the reactants and conditions. The zwitterion may dimerize or polymerize or react with the carbonyl compound to form an ozonide ... 

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