Alkenes, Alkynes Pt 3

Alkenes: Oxidation Ozonolysis

Dihydroxylation with OsO4

Alkenes: Oxidation Hydroboration oxidation

Alkenes: Oxidation Cold, alkaline KMnO4

acidic KMnO4

Polymerization of Alkenes • Polymers are large molecules that contain a large number of repeating units of a small molecule (monomer). • Biopolymers are typically synthesized by organisms. • Synthetic Polymers are made in organic laboratories.

Polymerization of Alkenes Alkenes can be used as a monomeric unit to form chain-growth polymers

styrene

polystyrene n

Polymerization of Alkenes

Polymerization of Alkenes For the polymerization, electrophilic addition reactions can be used. BF3

F3B

In the initiation step an electrophile (BF3) adds to the alkene to form a carbocation intermediate.

Polymerization of Alkenes Subsequent propagation steps grow the polymer until all monomers are consumed.

F3B

+

F3B

Polymerization of Alkenes Termination can also be accomplished by adding a nucleophile.

Nu F3B n Nu F3B n

Polymerization of Alkenes An alternative way to initiate polymerization is starting with a radical initiator. RO OR

D (hn)

2 RO radicals

The radical adds onto the alkene to form a new radical. Propagation is accomplished via subsequent radical additions. R

R

R

RO RO

β-ELIMINATION REACTION

PREPARATION OF ALKENES

Preparation of Alkenes • • • •

β-Elimination Reactions Dehydrogenation of alkanes Dehydration of alcohols Dehydrohalogenation of alkyl halides

Dehydrogenation of Alkanes

Dehydration of Alcohols

Zaitsev’s Rule

Dehydrohalogenation of RX

ADDITION & DIELS-ALDER REACTIONS

CONJUGATED DIENES

Reaction of Conjugated Dienes

• undergo two-step electrophilic addition reactios just as do simple alkenes • 1,2 & 1,4-addition

Reaction of Conjugated Dienes

CH2 CH CH CH3 Less Substituted Double Bond (Secondary carbocation)

CH2 CH CH CH3 More Substituted Double Bond (Primary carbocation)

Diels-Alder Reaction: Cycloaddition +

ADDITION, OXYDATION, & ACIDITY OF TERMINAL ALKYNES

REACTION OF ALKYNES

Reactivity of Alkynes

Hydrohalogenation

Hydrohalogenation

Halogenation

Hydration

Hydration of Alkyne & Tautomerism

Draw the ENOL tautomers of the following ketones:

Catalytic Reduction

Oxidation

Acidity of Terminal Alkynes HC CH + NH2

HC C

+ H3N

Acidity of Terminal Alkynes

-FIN-