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Understanding Dehydration of Alcohols: Mechanisms and Reactions

Learn about the mechanisms and reactions involved in dehydrating alcohols to form alkenes through elimination processes. Explore key concepts like E1 reaction, SN1 reaction, dehydrohalogenation, isotope effect, element effect, and synthesis procedures.

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Understanding Dehydration of Alcohols: Mechanisms and Reactions

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  1. Dehydration of Alcohols

  2. Elimination Reactions Y C - C X To make C=C need to eliminate X, Y.

  3. Y C - C X 3 ways to break 2 bonds 1. Concerted (x and y leave same time) 2. X leaves first 3. Y leaves first

  4. Leaving Group

  5. E1 Reaction R-X R+ + X- Alkene + H+

  6. E1 1 bond at a time Elimination

  7. R+ SN1 E1 Rearrangement Substitution Elimination

  8. SN1 E1

  9. Dehydrohalogenation X C - C H Strong base

  10. What is the mechanism of dehydrohalogentation? C-D bond stronger than C-H bond.

  11. Isotope Effect NaOEt NaOEt kH/kD = 7

  12. Isotope effect shows that C-H bond broken in the transition state.

  13. Element Effect Change Element I > Br > Cl

  14. SYN vs. ANTI Elimination Same Side Opposite Side

  15. Transition State Energy Starting Material Product

  16. E 2 2 Bonds at a time Elimination

  17. Procedure

  18. Put cyclohexanol and sulfuric acid in round bottom flask • Fractional Distillation (steam distillation) collect distillate 80-85o • Dry product with K2CO3 • 4. Distill

  19. Distil immiscible liquids PT = PA + PB (Steam Distillation)

  20. Baeyer Unsaturation Tests Potassium Permanganate KMnO4

  21. Bromine and Cyclohexene

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