Variational biorthogonal valence bond descriptions of 1,3‐dipoles

Abstract The variational biorthogonal valence bond method is applied to the π‐electrons of six 1,3‐dipoles (CH2N2, HCNO, CH2NHO, N2O, O3, NO2). The results are compared with those from other valence bond techniques, including a detailed comparison with the spin‐coupled valence bond approach. For CH2N2, HCNO, CH2NHO, and N2O, zwitterionic structures are predicted and it is shown that the variational biorthogonal valence bond method leads to orbitals and configuration weights which are essentially indistinguishable from those of the spin‐coupled valence bond method. However, for O3 and NO2 the techniques give contradictory results. The biorthogonal valence method predicts O3 and NO2 to be spin‐paired diradicals. Evidence from other calculations on O3 is discussed. © 1994 by John Wiley & Sons, Inc.