CHEM 333 Alkene addition reactions

Hydrogenation of alkenes

-Reagents: H2 over metal catalyst (Pd/Pt)

-Surface reaction

-Syn addition from the less crowded face

RESULTS IN: alkane

hydrogenation example

hydrohalogenation of alkenes

Where an alkene reacts with Hx to make an alkyl halide

-Reagents: HCl, HBr etc.

-Addition

-Carbocation intermediates, rearrangements possible

-Markovnikov addition

-No stereochemical preference

RESULTS IN: alkyl halide

Markovnikov's Rule

hydrogen will add to the least substituted carbon of the double bond

hydrohalogenation of alkene example

Hydration of alkenes

-makes ALCOHOL from an alkene

O-OH adds across the double bond

-three types of this reaction:

*acid-catalyzed hydration

*oxymercuration-demercuration

*hydroboration-oxidation

Acid-catalyzed hydration of alkenes

REAGENT: H2SO4 (aq)/H2O

-Markovnikov's Rule

-C+ intermediate/ possible rearrangement

results in alcohol formation

Acid-catalyzed hydration of alkene example

Oxymercuration-Demercuration

REAGENTS: Hg(OAc)2 (aq), NaBH4

-Markovnikov's Rule

-No C+ intermediate formed

-mechanism not needed

results in alcohol formation

Hydroboration-Oxidation

REAGENTS: BH3, H2O2, OH-

-ANTI Markovnikov

-Syn addition

results in alcohol formation

Hydroboration-Oxidation of alkene example

halogenation of alkenes

Addition of halogens to an alkene forming a vicinal dibromide

REAGENT: Br2

-Anti addition NOT syn addition

-bromonium ion intermediate forms

halogenation of alkenes example

Conversion of alkenes to vicinal halohydrins

REAGENTS: Br2, H2O

-BrOH adds across the double bond

-anti addition

-OH will add on more substituted carbon

Epoxidation of alkenes

REAGENTS: mcpba or RCO3H

-creates an epoxide

Ozonolysis of alkenes

REAGENTS: Ozone, DMS

-oxidative cleavage

-ketones and aldehydes produced

dihydroxylation of alkenes

REAGENTS: OsO4, NaHSO3, H2O

Alt reagents: KMnO4, NaOH, cold

-no mechanism

Anti-Markovnikov hydrohalogenation of alkene

REAGENTS: Hx, peroxide (ROOR)

-radical reaction w/ homolytic arrows