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.