CHEM 2311H LT 10

Alkene Reaction

hydrohalogenation

• adds H and X

• for asymmetrical alkenes: halogen adds Markovnikov

• for HBr: halogen adds anti-Markovnikov

• produces enantiomers

acid catalyzed hydration

• addition of H/OH

• Markovnikov regioselectivity

• more substituted alkene = faster rxn

• Dilute acid favors formation of the alcohol, while concentrated acid favors the alkene

• produces enantiomers

oxymercuration-demurcuration

• alternative to add water to alkenes

• proceeds through mercurnium ion intermediate

• adds Markovnikov

hydroboration-oxidation

• adds H and OH with anti-Markovnikov regioselectivity

• stereoselective for syn addition

• proceeds via a concerted process, in which borane is attacked by a pi bond, triggering a simultaneous hydride shift.

  
  

catalytic hydrogenation

• addition of H₂ across alkenes with a metal catalyst

• syn addition stereoselectivity

• heterogeneous catalyst: Pd or Pt metal which doesn’t dissolve in rxn medium

• homogeneous catalyst: dissolves in rxn medium (Wlkinson’s catalyst)

halogenation

• addition of Cl₂ or Br₂ to alkenes

• Bromination proceeds via a bridged intermediate, called a bromonium ion, which is opened by an SN2 process that produces an anti addition.

• In the presence of water, the product is a bromohydrin or a chlorohydrin, and the reaction is called halohydrin formation

• prodcues one meso product

halohydrin

• product of the addition of Cl₂ or Br₂ to alkenes in the presence of H₂O

• anti addition

• regioselective: halide adds to less sub C, OH adds to more sub C

haloethers

• alcohol solvents act as nucleophile to Cl₂ or Br₂ addition

Syn-dihydroxylation

• syn addition of OH and OH across the alkene

• Syn dihydroxylation can be achieved with osmium tetroxide or potassium permanganate.

epoxidation

• epoxides: can be synthesized when an alkene is treated with a peroxyacid, RCO₃H

• preserves stereochemistry

anti-dihydroxylation

• anti addition of OH and OH across the alkene

• multi-step epoxide = diol

ozonolysis

• a process of oxidative cleavage of alkenes

ozonolysis reagents

1. O₃

2. DMS or Zn/ H₂O

anti dihydroxylation reagents

1. RCO₃H

2. H₃O⁺

epoxidation reagents

RCO₃H (MCPBA)

syn dihydroxylation reagents

KMnO₄ or OsO₄/NMO

halohydrin formation reagents

Br₂, H₂O

Bromination/ chlorination reagents

Br₂/ Cl₂

catalytic hydrogenation reagents

H₂, Pt

hydroboration-oxidation reagents

1. BH₃ THF

2. H₂O₂, NaOH

Oxymercuration-demurcuration reagents

1. Hg(OAc)₂, H₂O

2. NaBH₄

acid-catalyzed hydration reagents

H₃O⁺ (dilute H₂SO₄)

radical addition of HBr reagents

HBr, ROOR

hydrohalogenation reagents

HX