Journal of Molecular Structure: THEOCHEM, 136(1-2), 121-138. Elsevier
سنة النشر:
1986
الوصف:
The thermal and photochemical [1,3]-H shift in propene and [1,5]-H shift in 1,3-pentadiene have been investigated by means of ab initio calculations. The suprafacial and antarafacial transition states are compared with a transition state (TS) of C2v symmetry, which results from a shift of the migrating hydrogen atom in the plane of the carbon skeleton (planar shift). Full geometry optimizations were performed at the ab initio level of computation using the restricted and unrestricted Hartree—Fock formalism with a 3-21G basis set. All structures were characterized by a complete vibrational analysis. Final state energies were calculated from a configuration interaction among the leading configurations. The effect of all other configurations was treated through a second-order perturbation. The thermal shifts are found to proceed according to the rules of Woodward and Hoffmann, i.e. an antarafacial [1,3]-H shift in propene and a suprafacial [1,5]-H shift in pentadiene. In both cases a second TS of C2v symmetry is found close in energy to the first. These TSs must be described with an open-shell configuration. For the photochemical process, both shifts are found to proceed through a TS of C2v symmetry. This TS correlates with a twisted conformation of the reactant via a planar shift.
