Ionic association mechanisms, synthetically

The reaction of ozone with saturated hydrocarbons has been a subject of renewed interest in recent years. Two papers in this section are concerned with this subject, while a third deals with the analogous reaction of organosilicon compounds. These studies are of both synthetic and mechanistic importance and are perhaps most closely associated with the general theme of this symposium since they inevitably involve the question of their relationship to autoxidation processes. The question of the mechanism of these saturated hydrocarbon-ozone reactions is presently an active subject with ionic, free radical, and insertion processes all being considered. 

For isolated sites, we have found that both Tl and T3 compensating cations are located in the side pocket area. In synthetic mordenites, at least two sites in side pockets are substituted by Al ( 2.5). Since the binding of Na at T3 is favored with respect to that at Tl, the three short Na-O bonds indicated by experiment (to Ol, Ol and 09) can then be related to our calculated values at T3. In the presence of a second Na to compensate Al in Tl, one can expect that the mutual repulsion of the two cations will modify their position. Taking into account their relative stability, the experimental evidence that the other cation is pushed downward to the main cavity (Simoncic and Armbruster 2004) is supported by om results. Moreover we could argue further about Na-MOR with 6 Al per unit cell this Al content would imply the presence of three (Na, Al) pairs in the side pockets (presumably two at T3 and one at Tl). In this situation, one may expect that only two cations will remain inside the pocket, whereas the third one will be pushed outside due to cation-cation repulsion (this argument is verified by classical molecular mechanics simulations using Cerius2 associated with the cvff-aug-ionic force field (Demuth et al. 2001). 

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