L4 The FMO Approach

FMO approach - thermal and photochemical orbital energies

Drawing MO diagrams in pi systems recap

Easy way to construct the HOMO and LUMO orbitals

For HOMO phase is the same across pi bonds and changes across sigma bonds

For LUMO phase is the same across sigma bonds and changes across pi bonds

FMO approach to the Diels-Alder reaction

inverse electron demand is the electrons flowing the other way round so the HOMO/LUMO have been flipped.

constructive overlap means feasible

FMO approach to 3,3 sigmatropic rearrangement

How do you shade the sigma lobes for the HOMO/LUMO

The shading follows the same rule as for pi - in the HOMO, alternate across a sigma bond (i.e. the bond connecting the pi to the sigma) and in the LUMO keep shading the same across the sigma bond. Sigma bonds that are being formed must have the orbitals be in the right phases to form the bond.

FMO Approach: [2,3]-Sigmatropic Rearrangement

FMO approach: Thermal Electrocyclic Ring-Opening

FMO approach for photochemical electrocyclic ring closure