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Chapter 16 & 17 Discussion

Chapter 16 & 17 Discussion. Meso = identical. Endo and exo are meaningless without substitutents to provide frame of reference. diene. dienophile. Recognize that this is a Diels Alder reaction by the diene and dienophile (on the right). 2) Draw a cyclohexene ring.

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Chapter 16 & 17 Discussion

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  1. Chapter 16 & 17 Discussion

  2. Meso = identical Endo and exo are meaningless without substitutents to provide frame of reference

  3. diene dienophile Recognize that this is a Diels Alder reaction by the diene and dienophile (on the right) 2) Draw a cyclohexene ring 3) Build models of the possible isomers that could result from the cycloaddition 4) Use resonance to help predict regioisomer 5) Temperature for endo/exo preference.

  4. endo exo 3) Build models of the possible isomers that could result from the cycloaddition 4) Use resonance to help predict regioisomer 5) Temperature for endo/exo preference.

  5. Endo and exo + enantiomer + enantiomer Exo (thermodynamic product) Endo (kinetic product)

  6. ? Recognize that this is a Diels Alder reaction by the diene and dienophile (on the right) 2) Draw a cyclohexene ring 3) Build models of the possible isomers that could result from the cycloaddition 4) Use resonance to help predict regioisomer 5) Temperature for endo/exo preference.

  7. Four possible regioisomers and diastereomers (+ enantiomers)

  8. Resonance contributors show which regioisomers will form

  9. Regiochemistry is established. How about endo or exo?

  10. ?

  11. No meta.

  12. Problem:Diels-Alder Reactants?

  13. Flat, cyclic, conjugated pi system and 4n + 2 pi electrons

  14. Aromatic if 2, 6, 10, 14, 18 pi electrons….. Anti-aromatic if 4, 8, 12, 16, ….. pi electrons If neither then not aromatic or anti-aromatic. Anti-aromatic more stable than expected. Anti-aromatic – less stable and likely will not form at all.

  15. Cyclopropenyl anion 4 pi electrons. Antiaromatic

  16. Aromatic?

  17. Cyclopentadienyl anion 6 pi electrons, aromatic

  18. Aromatic?

  19. Azulene Yarrow chamomile 10 pi electrons aromatic Lactariusazulene

  20. Naphthalene aromatic : cyclic, 10 electrons, flat, conjugated

  21. naphthalene Azulene Why is naphthalene nonpolar and azulene polar?

  22. Aromatic, anti-aromatic or neither?

  23. Aromatic, anti-aromatic or neither? 8 pi electrons Depends on conformation. If flat and fully conjugated, antiaromatic!!!! Lower energy conformation (than anti-aromatic) is not flat

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