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Title. Cycloaddition. Electrocyclization. Pericyclic Reactions. Ethylene. Ethylene p -Molecular Orbitals. 171 nm 167 kcal/mol. IR. visible. UV. 800 nm. 400 nm. 200 nm. Ethylene/Butadiene. 1,3-Butadiene from Ethylene . Butadiene. 1,3-Butadiene p -Molecular Orbitals. 214 nm

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  1. Title Cycloaddition Electrocyclization Pericyclic Reactions

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

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

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

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

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

  7. Allyl Cation The Allylic System: Allyl Cation

  8. Allyl Radical The Allylic System: Allyl Radical

  9. Allyl Anion The Allylic System: Allyl Anion

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

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

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

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

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

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

  19. Electrocyclizations Electrocyclizations

  20. Butadiene-Cyclobutene 1,3-Butadiene-Cyclobutene

  21. (E,E)-Butadiene-Cyclobutene (E,E)-1,3-Butadiene-Cyclobutene

  22. (E,Z)-Butadiene-Cyclobutene (E,Z)-1,3-Butadiene-Cyclobutene

  23. (E,Z,E)-Hexatriene-Cyclohexadiene (E,Z,E)-1,3,5-Hexatriene-Cyclohexadiene

  24. (E,Z,E)-Hexatriene-Cyclohexadiene Orbitals (E,Z,E)-1,3,5-Hexatriene-Cyclohexadiene Orbitals

  25. Electrocyclization Summary Electrocyclizations

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

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