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Valence Bond Structures for the D2h Isomer of N2O4 and Some Isomers of S3O2 and S3O

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journal contribution
posted on 09.07.2007 by Richard D. Harcourt
The construction of valence bond structures of the increased-valence type is re-described for the D2h isomer of N2O4 and applied to obtain the corresponding valence bond structures for isomers of S3O2 and S3O, each of which has at least one six-electron four-center bonding unit. It is discussed how the S−O and S−S bond properties that are associated with the S3O2 and S3O increased-valence structures are in qualitative accord with the calculated bond lengths. The qualitative six-electron four-center molecular orbital theory for the symmetrical O−S−S−O component of each S3O2 isomer is related to the increased-valence structure for the six electrons. An increased-valence structure for the lowest-energy S3O2 isomer is equivalent to a restricted form of resonance between 16 Lewis-type valence bond structures. The two types of S−S bond length are used to provide empirical estimates of the weights for these Lewis structures and are compared with those obtained from the results of STO-6G valence bond calculations for the 3Σ- ground state of SO.