Alkene Reactions

HX Addition to an alkene

• know mechanism

• carbocation intermediate (want the most stable 3>2>1)

• X attaches to more subsituted Carbon of double bond

• Markovnikovs rule- rich get richer (Hs)

• 2 steps: protonation of double bond, Nu attack of halide to carbocation

• strongest acid reacts fastest (HI>HBr>HCl>HF)

Addition of HBr in Peroxides

• anti-markovnikov addition - rich get Br

• only for HBr

• peroxides (ROOR)

Acid catalyzed hydration of alkene

• alkene —> alcohol

• 3 steps: protonation of double bond to form carbocation, Nu attack of H2O, deprotonation of the alcohol

• markovnikov addition - rich get H, more substituted get + charge

• Reactant: alkene + H3O+

• Product: alcohol + H3O+

• Must know mechanism

Hydroboration/oxidation

• Addition of OH and H to an alkene

• 2 steps: BH3, H2OO2, OH

• Anti-markovnikov addition - rich get OH

• syn addition - OH and H added to same side of double bond

Halogenation

• addition of X2 to an alkene to form a vic-halide

• anti/trans addition of Xs, added to opposite sides of the double bond

• symmetrical addition (2 X being added)

• Reactant: alkene

• Reagent: X2

• Product: vic-dihalide

Halohydrin formation

• addition of X and OH to alkene

• reactant: alkene + X2

• Reagent: water

• Product: alkene with X and OH

• Anti/trans addition of X and OH (Opposite sides of double bond)

• OH goes on more substituted C, rich get richer with H

• Unsymmetrical addition (X and OH)

Catalytic Hydrogenation Reaction

• symmetrical addition of H2

• reagent is always H2

• H2 molecules add across the double bond

• Coefficient is number of double bonds

• syn addition (Hs added to same side)

• requires a catalyst (Ni, Pt, Pd)

Epoxidation formation

• reactant: alkene

• Reagent: peroxyacid or mCPBA

• product: epoxide ring

• double bond is replaced with two new C-O bonds

Anti-dihydroxilation

• addition of two OH groups to where the double bond was

• forms anti-diol - OH groups have opposite stereochemistry

• + enantiomer'

• mechanism: occurs through epoxide ring opening

• reagents: RCO3H or mCPBA / H2O (H, OH)

Syn-dihydroxilation

• addition of two OH groups to where the double bond was

• forms syn-diol - OH groups have same stereochemistry (cis)

• goes through osmate ester (happens in 2 distinct steps)

• reagents: 1. KMnO4/2.H2O,OH or 1.OsO4/2.NaHSO3/H2O

Ozonoylsis

• ozone will break double bond to make aldehydes and ketons

• 2 conswencutive reactions:

  • 1. O3 / 2. Zn,H2O