Perturbational Molecular Orbital Theory PMO Applied to Oxetane Formation

Perturbational Molecular Orbital Theory PMO) Applied to Oxetane Formation 

Using PMO theory, it is possible to estimate the relative activation energy of reactions by assuming some reasonable structure for the transition state and then using perturbation theory to calculate the difference between the energy of the transition state and the energy of the reactants/ °  

For oxetane formation from formaldehyde and ethylene, we should consider the following four transition states and intermediates for the reaction 

When more than two orbitals are involved, the energy change must take into account all important orbital interactions. This will be illustrated for the formaldehyde-ethylene case following the method of Herndon and Giles. If we assume the bonds are half-formed in the transition state, then the exchange integral y is just equal to ij3. Since j3 has a value of about 40 kcal/mole, then 

For the F(n E(iT ) interaction only one electron is involved. For the E(ir)-F(n) interaction there are three electrons involved Two are lowered in energy and one is increased by the same amount. The others are lowered, so that there is a net one electron stabilized  

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