Dehydration of Alcohols

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

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

Leaving Group

Base Removes Proton

Animation

R-XR + + X - Alkene + H + E1 Reaction

Elimination 1 bond at a time E1

Substitution Elimination Rearrangement SN1SN1 E1 R+R+

SN1SN1

C - C X H Strong base Dehydrohalogenation

C-D bond stronger than C-H bond. Mechanism of Dehydrohalogenation

NaOEt k H /k D = 7 Isotope Effect

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

Change Element I > Br > Cl Element Effect

Same Side Opposite Side SYN vs. ANTI Elimination

Example

Animation

Product Starting Material Energy Transition State

Elimination 2 Bonds at a time E2

Procedure

1.Put cyclohexanol and sulfuric acid in round bottom flask 1.Fractional Distillation (steam distillation) collect distillate o 3.Dry product with K 2 CO 3 4. Distill Procedure

P T = P A + P B (Steam Distillation) Distil immiscible liquids

Potassium Permanganate KMnO 4 Baeyer Unsaturation Tests

Addition of Bromine

Bromine and Cyclohexene

Animation