1. More on: Molecular Orbitals Pericyclic Reactions Electrocyclic Reactions

2. Pi Bonding MO (bond along x-axis; orbitals in xy plane) x y z mirror in yz plane Symmetrical mirror plane (yz)

3. Pi Bonding MO (bond along x-axis; orbitals in xy plane) x y z rotate 180 o about z-axis in xy-plane

4. Pi Bonding MO (bond along x-axis; orbitals in xy plane) x y z Antisymmetric about the C 2 axis

5. Pi Antibonding MO (bond along x-axis; orbitals in xy plane) x y z mirror in yz plane Antisymmetric mirror plane (yz)

6. Pi Bonding MO (bond along x-axis; orbitals in xy plane) x y z rotate 180 o about z-axis in xy-plane Symmetric about C 2 axis

7. Pi Bond MO MirrorC 2 - axis A S Bonding S A Antibonding node

8. Allylic Resonance Energy of an isolated p-orbital allyl cationallyl radicalallyl anion bonding -   0 nodes SA anti-bonding -    2 nodes SA non-bonding -   1 node AS

9. M.O.s of 1,3-Butadiene Highest Occupied Molecular Orbital Lowest Unoccupied Molecular Orbital Energy of isolated p-atomic orbital (A.O.) bonding M.O. -  2 HOMO AS bonding M.O. -  1 SA anti-bonding M.O. -  3 * LUMO SA anti-bonding M.O. -  4 * AS

10. SA AS SA HOMO LUMO Orbital Symmetry in the Diels-Alder Reaction Equal HOMO-LUMO Energy Difference

11. AS SA AS HOMO LUMO AS SA EWG Diels-Alder Reaction with a Deactivated Dienophile EWG Lowers LUMO Energy

12. Dienophile LUMO (  3 *) Diene HOMO (  2 ) The Diels-Alder Reaction Transition State EWG

13. HOMO thermal rxn. h EE HOMO photochemical rxn. Photochemical Excitation in 1,3-Butadiene

14. 1,3-Butadiene Cyclobutene Conrotatory Disrotatory h 22 3*3*

15. but one cyclobutene is just like another cyclobutene enter stereochemistry

16. 1,3-Butadiene Cyclobutene Conrotatory Disrotatory h 22 Me HH H H 3*3* H H

17. Thermal Con Thermal Con h Dis h Dis Stereocontrol in the 1,3-Diene Cyclization E,E E,Z trans cis