ROSO. Can. J. Chem. 56,1093 (1978. Some nb-i~lirio valence-bond wave-functions are reported for the n-electrons of the groundstates of 0 3 , NOz-, and CHzNz. Examination of these wave-functions provides further support for the hypothesis that, for the ground-states of many electron-excess molecules, important valence-bond structures are those that are compatible with the electroneutrality principle, i.e. they carry either small or zero formal charges on each of the atoms. For O3 and CHzNz, the important valence-bond structures with zero atomic formal charges are Each of these structures has a 'long-bond' between non-adjacent atoms. The significance of 'long-bond' (or spin-paired diradical) structures for the electronic mechanism of 1,3-dipolar cycloaddition reactions is discussed and 'increased-valence' descriptions of the electronic structure of each molecule are presented. Some comments on the utility of 'increased-valence' structures are provided. [Traduit par le journal]
AbstractsFor each of HNO, FNO, LiNO, LiON and HFZ-, ab initio valence-bond wave functions are reported for the four-electron three-center bonding unit which involves one of the following sets of atomic orbitals: (a) NXg-bond ( X = H, For Li) and oxygen 2pn'; (b) LiO u-bond and nitrogen 2~7~' ; (c) hydrogen 1s and fluorine 2pu. Six S = 0 valence-bond structures pertain for this type of bonding unit. For HFZ-and FNO, the calculated bond-eigenfunction coefficients for some of these valencebond structures differ appreciably according to whether the Slater determinants include only the electrons of the four-electron three-center bonding unit, or all of the valence-shell + inner-shell electrons. For HNO, LiNO, and LiON, the all-electron and all valence-shell electron calculations generate similar sets of bond-eigenfunction coefficients. For each of the nitrosyl systems, the bond-eigenfunction coefficient with largest magnitude is calculated to be that for which zero atomic formal charges occur in the valence-bond structure. Qualitative valence-bond and "increasedvalence" descriptions of the bonding are presented.
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