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Pericyclic Reactions Title Cycloaddition Electrocyclization.

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Presentation on theme: "Pericyclic Reactions Title Cycloaddition Electrocyclization."— Presentation transcript:

1 Pericyclic Reactions Title Cycloaddition Electrocyclization

2 Ethylene  -Molecular Orbitals 171 nm 167 kcal/mol 400 nm800 nm200 nm visibleUV IR Ethylene

3 1,3-Butadiene from Ethylene Ethylene/Butadiene

4 214 nm 133 kcal/mol 1,3-Butadiene  -Molecular Orbitals 400 nm800 nm200 nm visibleUV IR Butadiene

5 258 nm 109 kcal/mol 1,3,5-Hexatriene  -Molecular Orbitals 400 nm800 nm200 nm visibleUV IR Hexatriene

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

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

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

12 Allyl Cation DA [4+2]-Cycloaddiitions

13 Diels-Alder Reaction: Mechanism Diels-Alder Mechanism

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

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

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

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

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

19 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 n=1,2,3,4…thermal photochemical 4ncondis 4n+2discon

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


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