On definition of electronegativity within the framework of MO methods

The possibility of generalization of the electronegativity concept to valence states of atom in molecule has been studied by semiempirical CNDO and INDO approximations. It is shown that the concept of electronegativity as the property of a given atom in molecule can be defined only on the basis of the simplest CNDO approximation.

Calculation of CNDO Characters Orders with Account of Virtual Pars Orbital Contributions

The contribution of virtual pars orbitals to the occupied molecular orbitals is taken into account in the CNDO approximation. On this basis a new index ϱ̄L is introduced, which is similar to the character order ϱL in the π-electron approximation. The calculated values of ϱ̄L for the 19 compounds under investigation correlate well with the experimental bond lengths, as well as with a number of other physical and chemical properties.

CNDO–MO Study of the Ozonide Ion and Related Species

The unpaired electron in the ozonide ion (O3−) is expected to occupy an antibonding molecular orbital; yet published experimental results indicate a shorter bond length and larger force constants than in neutral ozone. Molecular orbital calculations in the CNDO approximation are reported for this ion and related species (O3, SO2, SO2−, OF2+, OF2), using both the CNDO/2 and CNDO/BW parametrizations. Both methods predict that the bond lengths in O3− are 0.04 Å longer than in O3, in agreement with qualitative molecular orbital theory, and that the bond angle is 1° less than in O3. The CNDO/BW method predicts that the electron affinity of O3 is higher than that of the O atom, in agreement with experiment, since a stabilizing exchange effect outweighs the antibonding nature of the orbital occupied by the extra electron.