Zusammenfassung der Ressource
Reactions of Alkenes
- Electrophilic Additions
- Addition of HYDROGEN HALIDES
Anlagen:
- Free Radical Addition of HBr:
Anti-Markovnikov Addition
- Does NOT
include HCl or HI
- Peroxides give rise to
free radicals that
initiate addition
Anmerkungen:
- The oxygen-oxygen bonds are relatively weak so it can break to give any two alkoxy radicals
- Alkoxy radicals (R - O) initiate the anti-Markovnikov addition of HBr
- Addition of Water: Hydration
Anmerkungen:
- Adding excess H2O to drive the equilibrium toward the alcohol
- Follows Markovnikov's rule
- May take place with rearrangement
- Hydration by
Oxymercuration-Demercuration
Anmerkungen:
- Makes alcohols
- Follows Markovnikov's orientation
- No free carbocation is formed so no rearrangements or polymerization can occur
- Reagent used is mercuric acetate, Hg(OCOCH3), which is abbreviated as Hg(OAc)2
- Alkoxymercuration-Demercuration
Anmerkungen:
- Alcohol solvent
Alcohol is the nucleophile that attacks the mercurinium ion
- Makes ethers
- Follows Markovnikov's orientation
- Hydroboration
Anmerkungen:
- Anti-Markovnikov's orientation
- BH3 adds to the double bond of an alkene to give an alkyborane
- Oxidation
Anmerkungen:
- H2O2 (peroxide) oxidizes the alkylborane to an alchol
- Addition of Halogens
Anmerkungen:
- Solvents must be inert to halogens
CH2Cl2-methylene chloride
CHCl3-chloroform
CCl4-carbon tetrachloride
- Anti-addition because the nucleophilic halide must do a back-side attack
- Halohydrins
Anmerkungen:
- Forms alcohols with a halogen on adjacent carbons
- Water is the solvent and nucleophile
- Back-side attack by the nucleophile ensures anti-addition
- Follows Markovnikov's orientation
- Catalytic Hydrogenation
Anmerkungen:
- Syn-addition
- A reduction with H2 gas adding across a double bond to produce an alkane
- Catalyst required is usually Pt, Pd, or Ni.
- Alkene is usually dissolved in alcohol, an alkane, or acetic acid
- Addition of Carbenes
Anmerkungen:
- Carbenes - uncharged, reactive intermediates that have a carbon atom with two bonds and two non-bonding electrons
- Forms cyclopropanes
- Simmons-Smith Reaction
Anmerkungen:
- Reagent is methylene iodide added to a zinc-copper couple (zinc dust). Also called a carbenoid.
- The cis or trans stereochemistry of the products is retained from the reactants
- Epoxidation
Anmerkungen:
- Converts alkenes into different functional groups
- Uses peroxyacids which are carboxylic acids with an extra oxygen atom
- cis or trans stereochemistry is retained from the reactant
- Acid-Catalyzed
Opening of
Epoxides
Anmerkungen:
- An acid protonates the epoxide and water, the nucleophile, attacks the protonated epoxide to open the ring and form the 1,2 diol (glycol)
- Anti-stereochemistry of hydroxyl groups
- Syn-Dihydroxylation
Anmerkungen:
- Both reactions will produce syn stereochemistry in the products
- Osmium Tetroxide
- Permanganate Dihydroxylation
- Oxidative Cleavage
- Permanganate
Anmerkungen:
- Break the C-C double bond to form carbonyl groups
- Aldehydes further oxidize to carboxylic acids
- Ozonolysis
Anmerkungen:
- Break C-C double bonds to generate carbonyl groups
- Aldehydes are not further oxidized
- Polymerization