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Conjugation

Conjugation. Which of the following compounds is conjugated?. Conjugation. Which of the following compounds is not conjugated?. Slides 4 and 5 are part of the same question. Butadiene. 2 conformations possible, both overall planar. Butadiene. Which conformation appears to be more stable?

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Conjugation

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  1. Conjugation • Which of the following compounds is conjugated?

  2. Conjugation • Which of the following compounds is not conjugated?

  3. Slides 4 and 5 are part of the same question.

  4. Butadiene • 2 conformations possible, both overall planar

  5. Butadiene • Which conformation appears to be more stable? a. s-cis b. s-trans c. neither

  6. Butadiene • Would forms A, C, and D contribute significantly? a. yes b. no This would be one explanation for the low degree of delocalization in dienes.

  7. Slides 8 9 and 12 pertain to the questions on slides 10 and 11.

  8. SpectroscopyUltraviolet-Visible (UV-Vis) • Many organic compounds absorb light at wavelengths below 300 nm. • e.g. ethylene,  - * transition, E = 173 kcal/mole,  = 165 nm

  9. SpectroscopyUltraviolet-Visible (UV-Vis) • As conjugation is extended, what is happening to the the HOMO-LUMO energy gap? a. increases b. decreases c. nothing

  10. SpectroscopyUltraviolet-Visible (UV-Vis) • As conjugation is extended, what will happen to the wavelength of absorption increases? a. increases b. decreases c. nothing • (E = hc/)

  11. Reactions of Conjugated CompoundsDienes:1,2- vs. 1,4-Addition • Which ion is more likely to form and why?

  12. Reactions of Conjugated CompoundsDienes:1,2- vs. 1,4-Addition • The numbering in this case has nothing to do with nomenclature. Instead the numbering indicates where the “pieces” of the electrophile attached. • Which alkene would be more stable, the 1,2 or 1,4 addition product? a. 1,2 addition product b. 1,4 addition product c. neither

  13. Reactions of Conjugated CompoundsDienes:1,2- vs. 1,4-Addition • Which C would be expected to have more partial positive charge? a. Y b. Z c. neither

  14. Reactions of Conjugated CompoundsDienes:1,2- vs. 1,4-Addition •  Which product will form faster? a. 1,2 addition product b. 1,4 addition product c. neither

  15. Diels-Alder Reaction • Could another product have formed?  a. yes b. no

  16. Diels-Alder Reaction • Diels-Alder reaction : addition of dienophile to diene is syn or anti? a. syn b. anti c. both d.neither

  17. Diels-Alder Reaction • Can the reaction occur in the s-trans conformation? a. yes b. no

  18. How many isoprene units are present in nepetalactone?

  19. Predict the major product of the following reaction.

  20. What is the major product for the following reaction?

  21. Which of the following is not a p molecular orbital if 1,3-butadiene?

  22. Which pmolecular orbital reduces the p bonding character between C2 and C3 of 1,3-butadiene (and is still a bonding MO)?

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