VARIATIONAL BIORTHOGONAL VALENCE-BOND DESCRIPTIONS OF 1,3-DIPOLES

The variational biorthogonal valence bond method is applied to the pi- electrons of six 1,3-dipoles (CH2N2, HCNO, CH2NHO, N2O, O-3, NO2). The results are compared with those from other valence bond techniques, i ncluding a detailed comparison with the spin-coupled valence bond appr oach. For CH2N2, HCNO, CH2NHO, and N2O, zwitterionic structures are pr edicted and it is shown that the variational biorthogonal valence bond method leads to orbitals and configuration weights which are essentia lly indistinguishable from those of the spin-coupled valence bond meth od. However, for O-3 and NO2 the techniques give contradictory results . The biorthogonal valence method predicts O-3, and NO2 to be spin-pai red diradicals. Evidence from other calculations on O-3 is discussed. (C) 1994 by John Wiley and Sons, Inc.