Organic Chemistry Reactions Overview

Reaction with Hydrobromic Acid (HBr)

• Example 1: 1-Butene + HBr

  • Alkene acts as a nucleophile, acid as an electrophile.
  • Hydrogen attaches to the primary carbon of the double bond.
  • A more stable secondary carbocation is formed.
  • Bromide ion attacks, creating a racemic mixture.

• Example 2: Alkene + HBr vs. HBr + Peroxides

  • Without Peroxides: Markovnikov addition where bromine attaches to the more substituted carbon.
  • With Peroxides: Anti-Markovnikov addition where bromine attaches to the least substituted carbon.

Cyclohexene Reactions

• Cyclohexene + Br2 (in CH2Cl2)

  • Anti-addition occurs, yielding a mixture of enantiomers.

• Cyclohexene + NBS

  • Radical reaction; bromine replaces an allylic hydrogen.

Alkanes and Bromine Reactions

• Alkane + Br2 (UV light)
  • Free radical substitution reaction; bromine attaches to the most substituted (tertiary) hydrogen.

Hydration of Alkenes

• Example: Alkene + Water + HCl
  • Acid catalyzed hydration results in alcohol formation.
  • Potential carbocation rearrangement for stability.

Hydrogenation of Alkenes

• Example: Cyclohexene + H2 (Metal Catalyst)
  • Converts alkene to alkane using syn addition.

Hydroboration-Oxidation

• Example: Alkene + BH3/THF + H2O2/NaOH
  • Adds OH to the least substituted carbon; syn stereochemistry.

Oxymercuration-Demercuration

• Example: Alkene + Hg(OAc)2 + NaBH4
  • Adds OH to the more substituted carbon without rearrangement.

Epoxidation and Diol Formation

• Example: Alkene + MCPBA

  • Forms epoxide, which can be converted to trans-diol with acid.

• Cis-diol Formation: OsO4 + NaHSO3 leads to cis-diol.

Alkyne Reactions

• Hydrogenation

  • Alkyne + H2 (Pt catalyst) → Alkane.
  • Alkyne + Na (liq. NH3) → Trans alkene.
  • Alkyne + H2 (Lindlar's catalyst) → Cis alkene.

• Hydroboration of Terminal Alkynes

  • Alkyne + R2BH → Aldehyde (via enol tautomerization).

• Mercury-catalyzed Hydration

  • Alkyne + HgSO4 (H2O, H2SO4) → Ketone.

SN2 Reactions

• Example: 2-Bromobutane + KI (acetone)
  • Iodide replaces bromide with inversion of configuration.

SN1 and E1 Reactions

• Example: 2-Bromobutane + Water
  • Leads to a mixture of products via carbocation intermediate.

E2 Reactions

• Example: 2-Bromobutane + Methoxide
  • Strong base promotes E2 elimination to form Zaitsev product.

Dehydration of Alcohols

• Example: Alcohol + H2SO4 (heat)
  • E1 elimination to form the most stable alkene.

Conversion of Alcohols to Alkyl Halides

• Using HX, PBr3, SOCl2
  • HX: SN1 mechanism, racemic mixture.
  • PBr3/SOCl2: SN2 mechanism, inversion of configuration.

Oxidation and Reduction

• Oxidation

  • PCC: Primary alcohol → Aldehyde.
  • Chromic acid: Primary alcohol → Carboxylic acid.
  • Secondary alcohol → Ketone.

• Reduction

  • NaBH4: Reduces aldehydes, ketones, acid chlorides to alcohols.
  • LiAlH4: Also reduces esters, carboxylic acids.

Grignard Reagents

• Example: Ketone + RMgBr
  • Forms alcohol with the addition of an R group.

These notes cover fundamental reactions and mechanisms in organic chemistry that are essential for understanding transformations and predicting products in synthesis problems.