Ch. 8 reagents/reaction

Hydrohalogenation

• Markovnikov: HBr, HCl, HI

  • Ex. Br placed @ most substituated

• Anti-markovnikov: HBr → ROOR

  • ex. Br placed @ least substituted

• When dilute HBr → carbocation

• can have carbocations

  • Prefer 3°>2°>1°

• chiral centre → enantiomer

Acid Catalyzed Hydration

• Markovnikov addition

• H3O+ or [H2SO4] or dilute H2SO4

• Add 1 OH → more sub.

• Add 1 H → least sub

• Has chiral → enantiomer

• Can have carbocations

Oxymercuration-Demercuration

• Markovnikov addition

• 1. Hg(OAc)2, H20/EtOH
  2. NaBH4

• Add 1 OH/nuc → more sub.

• Add 1 H → least sub.

• No carbocations

Hydroboration-Oxidation

• anti-Markovnikov addition (least sub.)

  • Syn addition → OH and H same

• BH3 . THF → H2O2, NaOH

• Add 1 OH → least sub.

• OH and H must be either BOTH Wedge or Dash.

  • opposite/trans = does not occur

• IF two new chiral centres are formed → syn addition occurs

  • No chrial → no enantiomer

Catalytic hydrogenation

• Syn additon

• heterogenous: H2 → Pt/Ni/Pd

• Double bond is removed with 2 H’s

• If chiral → pair of syn (both wedge/both dash) product

  • If no chiral → only one product

• If its meso → only one product

• homogenous: H2 → wilkinsons catalyst (RH with 3 PPh3 and 1 Cl)

  • asymmetric:

    • One chiral center → one ch3 wedge + ent

    • two chrial → both ch3 wedge + ent.

Halogenation and Halohydrin

Halogenation:

• Br2/Cl2

• add 2 - x across alkene

• If chiral → must be anti → one wedge one dash

• If starting material is Cis → anti addition + ent.

• If starting material is Trans → anti addition but no ent. since it is meso when flipped

Halohydrin:

• Br2/Cl2 → H2O

  • H2O = EtOH/EtNH2

• Add 1 OH → more sub.

• Add one X → least sub.

• Anti-addition → OH on wedge, X on dash + ent.

Dihydroxylation

Anti:

• RCO3H/CH3CO3H → H3O+

  • RCO3H → epoxide → H3O+ → trans/anti OH

• Add 2 OH across the alkene

  • One wedge one dash + ent.

Syn:

• OsO4 / KMnO4, NaOH →
  NMO or tert-butyl-OOH / cold

• Add 2 OH across the alkene

  • Both dash/wedge

• Using 1) OsO4 → can use:

  • 2) NaHSO3/H2O or

  • 2) Na2SO3/H2O

Oxidative cleavege/ Ozonolysis

• O3 → DMS or ZN/H2O

• double bond separates and produces two C=O (carbonyls).