1. Title
Pericyclic Reactions
Cycloaddition
Electrocyclization

2. Ethylene p-Molecular Orbitals
171 nm
167 kcal/mol
400 nm
800 nm
200 nm
visible UV IR

3. 1,3-Butadiene from Ethylene
Ethylene/Butadiene
1,3-Butadiene from Ethylene

4. 1,3-Butadiene p-Molecular Orbitals
214 nm
133 kcal/mol
400 nm
800 nm
200 nm
visible UV IR

5. 1,3,5-Hexatriene p-Molecular Orbitals
258 nm
109 kcal/mol
400 nm
800 nm
200 nm
visible UV IR

6. Butadiene Orbital Coeffients
Butadiene: Orbital Coefficients
Frontier
Molecular
Orbitals
FMOs

7. The Allylic System: Allyl Cation

8. The Allylic System: Allyl Radical

9. The Allylic System: Allyl Anion

10. Cycloaddition: Diels-Alder Reaction An Allowed [4+2] Cycloaddition

11. Diels-Alder Reaction: The Effect of Electron Withdrawing Groups

12. Allyl Cation DA
[4+2]-Cycloaddiitions

13. Diels-Alder Mechanism
Diels-Alder Reaction: Mechanism

14. Diels-Alder Endo Effect
Diels-Alder Reaction: The Endo Effect
Secondary Effect

15. What About a [2+2] Cycloaddition?
2+2?
What About a [2+2] Cycloaddition?
light (hn)

16. Thermally Allowed Cycloadditions
4n+2 Rule
Thermally Allowed Cycloadditions
4n+2 Rule
HOMOs
LUMOs A S 2 S A 4 S A 6
[4+2]=6 S A 8
[6+4]=10
[8+6]=14
4n+2; n=1,2,3,4…..

17. Photochemically Allowed Cycloadditions
4n Rule
Photochemically Allowed Cycloadditions
4n Rule
HOMOs
LUMOs A S 2 4 6 8
[2+2]=4
[4+4]=8
[6+6]=12
[8+8]=16
4n; n=1,2,3,4…..
and [2+6]=8; [8+4]=12

18. Summary of Cycloadditions
Thermal 4n+2
Photochemical 4n

19. Electrocyclizations
Electrocyclizations

20. Butadiene-Cyclobutene

21. (E,E)-Butadiene-Cyclobutene

22. (E,Z)-Butadiene-Cyclobutene

23. (E,Z,E)-Hexatriene-Cyclohexadiene

24. (E,Z,E)-Hexatriene-Cyclohexadiene Orbitals

25. Electrocyclization Summary
thermal
photochemical 4n
con
dis
4n+2

26. Violations “There are none!” Violations
Woodward and Hoffmann,The Conservation of Orbital Symmetry