Stretching and Breaking of Chemical Bonds Leading to Open–Shell Character of Molecular EIectronic Systems

This chapter focuses on the first implementation of the unrestricted Hartree-Fock theory capacity to establish criteria for forming, stretching, and breaking of chemical bonds. The main transformation of the bonds under stretching occurs in the W_rad region and concerns their radicalization that, in turn, generates the chemical activity of previously inactive bond atoms and enhances the latter the more the longer the bond becomes. Stretching and breaking of chemical bonds have been considered in the spirit of spin molecular theory of sp² nanocarbons and have been associated with changing correlation of valence odd electrons in response to enlarging interatomic distance. Chemical bonding, as was in the case of single bonds, evidently considerably influences the bond length, which in the case of alkenes and alkynes should be followed with enhanced reactivity of the compounds formed.