C_(70)Oxides and Ozonides and the Mechanism of Ozonolysis on the Fullerene Surface. ATheoretical Study

摘要

A series of ab initio calculations have been carried out to determine why the a,b- and c,c-isomers are themost commonly observed mono-oxides of C_(70)in ozonolysis reactions, when existing calculations in the literaturereport that these structures are not the most stable conformations. We show that the a,b- and c,c-isomers arethe two most stable structures on the C_(70)O_3potential energy surface, which suggests that the reaction pathwaytoward oxide formation must proceed via the corresponding ozonide structure. From our calculations, weoffer a mechanism for the thermally induced dissociation of C_(70)O_3that share the first two steps with thegeneral mechanism for ozonolysis of alkenes proposed by Criegee. We suggest further steps that involveC_(70)O_3losing O_2in its triplet or singlet state, thus leaving C_(70)Oin respectively. Apair of products in their singlet states seems to be more likely for the decomposition of a,b-C_(70)O_3, whichultimately leads to the closed a,b-C_(70)Oepoxide structure. For c,c-C_(O_3, the more thermodynamically favorableroute is the triplet channel, resulting in the triplet open c,c-C_(70)Ooxidoannulene structure, which maysubsequently decay to the singlet ground state c,c-C_(70)Oepoxide form. This finding offers an alternativeinterpretation of the experimental observations which reported an open d,d-C_(70)Ooxidoannulene structure asthe metastable intermediate.