,Addition of Alkenes

Halohydrin Addition

• Addition of a halogen (Br₂, Cl₂) and water to form a halogen with an alcohol.

• Bromonium ion and chloronium ion

• Trans product forms

• Anti-addition

Hydrohalogenation

• Addition of hydrogen and a halogen to form an alkene.

• Produces an alkyl halide

• Uses: HBr, HCl, HI

Hydration

• Addition of water to make an alcohol.

• Requires an acid (H₃O+)

• Syn and anti-addition.

  • Possible carbocation rearrangement

Oxymercuration-demercuration

• Addition of an alcohol and H to an alkene to form an alcohol.

• Follows markovnivkov’s rule.

• Opposite of hydrogenation

  • No rearragement & carbocation

  • Anti-addition

• Only 1 product

• Uses Hg(OAC)₂

Hydrobromination

• Addition of H and an alcohol to an alkene to form an alcohol.

• Follows anti-markovnivkov’s rule

• No carbocations → no intermediates

• Uses: 1. BH₃*THF, 2. Peroxide (H₂O₂), NaOH

Hydrogenation

• Addition of hydrogen (H₂)

• Syn-addition

• Needs a catalyst to speed up the rxn

• Uses: H₂, Ni, Pt, Pd

Halogenation

• Addition of Br₂, Cl₂, I₂ to form a dihalide.

• No carbocation formation.

• Bromonium ion and chloronium ion forms.

• Product is trans configured.

• Uses: Br₂ (mostly)

Halohydrin

• Addition of halogen (Br₂, Cl₂) and water to form a halogen and an alcohol.

• Anti-addition.

• Trans configured product forms with bromonium and chloronium ion intermediates.

Epoxidation

• Formation of an epoxide.

• Uses: MCPBA (meta chloroperoxybenzoic acid)

• Stereospecific

What determines the stability of an alkene?

• Energy level: lower energy alkenes are more stable.

• Heat of hydrogenation

• Heat of combustion

• Hyperconjugation: more substituted alkenes are more stable.

Which is more stable: a tetrasubstituted alkene or an monosubstituted alkene?

A tetrasubstituted alkene will be more stable than a monosub. alkene due to hyperconjugation.

• Electron donating groups can donate e^- into orbitals.

• Neighboring CH₃ groups overlap with neighboring p-orbitals.

Regiochemistry

Location and position of where changes take place in a reaction.

Markovnivkov’s Rule

The proton will be added to the least substituted region of a carbon in unsymmetrical alkenes.

Major product

Anti-markovnikov Rule

• Electrophilic addition to an alkene or alkyene.

Syn-addition

Same face addition

Anti-addition

Opposite face addition.