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

Mechanism

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

Elimination 1 bond at a time E1

Substitution Elimination Rearrangement SN1SN1 E1 R+R+

SN1SN1 E1 SN1

C - C X H Strong base Dehydrohalogenation

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

NaOEt k H /k D = 7 Isotope Effect

Isotope effect shows that C-H bond broken in the transition state. Bond Broken in Transition State

Change Element I > Br > Cl Element Effect

Same Side Opposite Side SYN vs. ANTI Elimination

E2 Animation

Product Starting Material Energy Transition State

Elimination 2 Bonds at a time E 2

Procedure

Put cyclohexanol and sulfuric acid in round bottom flask Fractional Distillation (steam distillation) collect distillate 80-85o Procedure

Dry product with K 2 CO 3

Distill

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

Potassium Permanganate KMnO 4 Baeyer Unsaturation Tests

Bromine Addition

Bromine and Cyclohexene

Br Bromonium Ion

Bromonium Ion Intermediate

Br - Mechanism

Animation