Chapter 7

Alkenes: Reactions and Synthesis

Goals

n   After this chapter, you should be able to:

–  Show various elimination preparations for alkenes

–  Give products for various addition reaction of:

•   Halogens

•   Water

•   Carbene

•   Hydrogen

–  Give products for reaction of alkene:

•   Cleavage

•   Radical polymerization

 

Introduction

n   Alkene are important because they can be used to synthesize

–  Alchohols   ROH

–  Alkanes      

–  Diols          HOC-COH

–  Carbonyl compounds C=O

–  Cyclo compounds 

–  Halides        R-X  where X=Cl, Br

–  Dihalides     X-C-C-X

–  Halohydrins  HO-C-C-X

 

Alkene Synthesis

n   Elimination Reactions –  Halogens with base

 

 

–  Alcohols with acid

 

 

 

 

 

 

Alkene: Addition of Halogens

 

 

 

 

The Bromonium Ion Intermediate

 

 

 

 

 

 

 

 

 

Halohydrin Formation

n   If another nucleophile is present, the bromonium ion can be intercepted.

 

 

 

 

 

 

 

 

 

 

 

 

Addition of Water to Alkenes

n   Acid catalyzed addition - H₃PO₄ and heat

 

 

 

 

 

Oxymercuration – Demurcuration

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hydroboration - Oxidation

n   Gives anti-Markovnikov addition of -OH

 

 

 

 

 

 

 

 

 

 

 

 

Carbene Addition

n   Carbenes are extremely reactive and can add to a double bond forming cyclopropane

 

 

 

 

 

 

Carbene Formation

 

 

 

 

 

 

 

 

 

Carbenoids: For Non-halogenated Cyclopropanes

n   The reagent is a metal-complex prepared by addition of CH₂I₂ and Zn(Cu) alloy in ether solvent. 

 

Carbene Addition

 

 

 

 

Reduction of Alkenes

n   Catalytic addition of hydrogen (H₂) 

 

 

 

 

 

Oxidation of Alkenes –
Diol formation

n   Hydroxylation

 

 

 

 

 

 

 

 

Ozonolysis–Double bond Cleavage

Di-aldehyde formation

 

 

 

 

 

 

 

 

Double Bond Oxidation–
(Poor to moderate  yield)

 

 

 

 

 

 

 

 

1,2 Diol Cleavage

 

 

 

 

 

 

 

 

 

 

 

 

 

The polymerization process of Addition or Chain-Reaction Polymerization consists of three steps:

n   Initiation – Typically benzoyl

peoxide

 

 

 

n   Propagation – Free radical propagate through double bonds

n   Termination – Radicals collide.

 

 Addition Polymerization 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cationic Polymerization–
Acid Catalyzed Polymerization

Polystyrene through acid catalyzed polymerization.

 

 

 

 

 

 

 

 

 

 

 

 

 

Give Products for the following

 

 

 

 

 

 

 

 

 

 

Draw all these structures!