The ozonolysis of ortho-xylene and its relevance to the history of the benzene problem

Authors
Citation
S. Wolfe et Z. Shi, The ozonolysis of ortho-xylene and its relevance to the history of the benzene problem, CAN J CHEM, 79(8), 2001, pp. 1278-1283
Citations number
25
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry
Journal title
CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE
ISSN journal
0008-4042 → ACNP
Volume
79
Issue
8
Year of publication
2001
Pages
1278 - 1283
Database
ISI
SICI code
0008-4042(200108)79:8<1278:TOOOAI>2.0.ZU;2-6
Abstract
Using B3LYP density functional theory in conjunction with the 6-311++G** ba sis set, the relative rates of the initial rate-determining attack of ozone upon the carbon-carbon bonds of o-xylene are found to be 4,5- congruent to 3,4- > 2,3- > 1,2-. With the assumption that the final products glyoxal (G ), methylglyoxal (M), and dimethylglyoxal (D) are determined by the site of the initial attack, and taking statistical factors into account, the ratio G:M:D is calculated to be 3:2:1. This is close to the value found experime ntally, and identical to the result predicted by the contention that two ne arly equivalent Kekule-Pauling valence bond (resonance) structures of o-xyl ene exist and each localized carbon-carbon double bond of these structures is oxidized at the same rate. Although Frontier Molecular Orbital theory al so predicts a 3:2:1 ratio of G:M:D, this theory incorrectly predicts that t he initial attack of ozone will take place at the 1,2- and 4,5- bonds, with 1,2-attack slightly preferred. These results are discussed in relation to a recent historical analysis of the benzene problem, and it is concluded th at since the products of ozonolysis of o-xylene are determined by the relat ive energies of the transition states leading to the four possible primary ozonides, these transition states should be the focus of theory.