Bil Andrzej, Latajka Zdzisław, Morrison Carole A
Faculty of Chemistry, University of Wrocław F. Joliot Curie 14, 50-383 Wrocław, Poland.
J Phys Chem A. 2009 Sep 10;113(36):9891-8. doi: 10.1021/jp9024798.
A series of ab initio calculations have been carried out to determine why the a,b- and c,c-isomers are the most commonly observed mono-oxides of C(70) in ozonolysis reactions, when existing calculations in the literature report that these structures are not the most stable conformations. We show that the a,b- and c,c-isomers are the two most stable structures on the C(70)O(3) potential energy surface, which suggests that the reaction pathway toward oxide formation must proceed via the corresponding ozonide structure. From our calculations, we offer a mechanism for the thermally induced dissociation of C(70)O(3) that share the first two steps with the general mechanism for ozonolysis of alkenes proposed by Criegee. We suggest further steps that involve C(70)O(3) losing O(2) in its triplet or singlet state, thus leaving C(70)O in its triplet or singlet state, respectively. A pair of products in their singlet states seems to be more likely for the decomposition of a,b-C(70)O(3), which ultimately leads to the closed a,b-C(70)O epoxide structure. For c,c-C(70)O(3), the more thermodynamically favorable route is the triplet channel, resulting in the triplet open c,c-C(70)O oxidoannulene structure, which may subsequently decay to the singlet ground state c,c-C(70)O epoxide form. This finding offers an alternative interpretation of the experimental observations which reported an open d,d-C(70)O oxidoannulene structure as the metastable intermediate.
已进行了一系列从头算计算，以确定为何在臭氧分解反应中，a,b - 和c,c - 异构体是C(70)最常观察到的单氧化物，而文献中的现有计算表明这些结构并非最稳定的构象。我们表明，a,b - 和c,c - 异构体是C(70)O(3)势能面上最稳定的两种结构，这表明形成氧化物的反应途径必定经由相应的臭氧化物结构进行。通过我们的计算，我们提出了一种C(70)O(3)热致解离的机制，该机制的前两步与Criegee提出的烯烃臭氧分解的一般机制相同。我们提出了进一步的步骤，涉及C(70)O(3)以三重态或单重态失去O(2)，从而分别使C(70)O处于三重态或单重态。对于a,b - C(70)O(3)的分解，一对处于单重态的产物似乎更有可能，这最终导致封闭的a,b - C(70)O环氧化物结构。对于c,c - C(70)O(3)，热力学上更有利的途径是三重态通道，导致三重态开放的c,c - C(70)O氧化轮烯结构，其随后可能衰变为单重态基态c,c - C(70)O环氧化物形式。这一发现为实验观察结果提供了另一种解释，实验观察结果报告了开放的d,d - C(70)O氧化轮烯结构为亚稳中间体。
