Molecular Orbitals and Pericyclic Reactions Woodward-Hoffmann Rules for Pericyclic Reactions -Reaction can occur only if the symmetries of the reactant MOs are the same as the symmetries of the product MOs The lobes of reactant MOs must be of the correct algebraic sign for bonding to occur in the transition state leading to product If the symmetries of reactant and product orbitals correlate,the reaction is symmetry-allowed.Reactions conditions are relatively mild If the symmetries of the reactant and product orbitals do not correlate,the reaction is symmetry-disallowed and there are no low energy concerted paths Fukui's Simplification Frontier Orbitals -Consider only the frontier orbitals-the highest occupied molecular orbital (HOMO)and the lowest unoccupied molecular orbital (LUMO)Woodward-Hoffmann Rules for Pericyclic Reactions •Reaction can occur only if the symmetries of the reactant MOs are the same as the symmetries of the product MOs • The lobes of reactant MOs must be of the correct algebraic sign for bonding to occur in the transition state leading to product • If the symmetries of reactant and product orbitals correlate, the reaction is symmetry-allowed. Reactions conditions are relatively mild • If the symmetries of the reactant and product orbitals do not correlate, the reaction is symmetry-disallowed and there are no low energy concerted paths Fukui’s Simplification – Frontier Orbitals •Consider only the frontier orbitals – the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) Molecular Orbitals and Pericyclic Reactions