Qualitative Potential Energy Surfaces. 5. Sigmatropic Shifts

The LCFC approach is used to generate the manifold of PE surfaces for radical-radical combination reactions and sigmatropic shifts. The effect of polarity on reaction rate and reaction toposelectivity is discussed. It is predicted that (a) within a series of structurally similar compounds, the rate of an i.j thermal sigmatropic shift increases as the migration framework and the migration group become a better donor-acceptor pair and (b) a thermal or photochemical sigmatropic shift occurs in the topochemical manner which couples the best donor-acceptor combination of migration framework and migrating group. Experimental data which support the qualitative theory are presented.