Organic Chemistry II Lecture Notes

Overview of Dienes and Their Reactions

• Formation of Dienes:

  • Created via elimination reactions.
  • Single or dihalide species can form conjugated dienes in the presence of potassium tert-butoxide.

• Reactions with Electrophiles:

  • HBr Addition to Dienes:
    • Produces 1,2 and 1,4 adducts.
    • 1,2 adduct: Kinetic product.
    • 1,4 adduct: Thermodynamic product.
  • Br2 Addition:
    • Yields kinetic (1,2) and thermodynamic (1,4) products.
    • Temperature influences product formation (low temp favors kinetic).

Diels-Alder Reactions

• Basic Reaction:

  • Conjugated diene reacts with dienophile forming cyclohexene.
  • New bonds form between diene and dienophile.

• Stereochemistry Considerations:

  • Cis dienophile: Remain cis in product.
  • Trans dienophile: Remain trans in product.

• Diene Conformation:

  • Diene must be in s-cis conformation.
  • Cyclic systems lock into s-cis conformation, speeding reaction.

Electrophilic Aromatic Substitution Reactions

• Benzene Reactions:

  • Low reactivity due to aromatic stability.
  • Electrophilic substitutions: Bromination, chlorination, nitration, sulfonation.

• Reduction of Benzene:

  • Full reduction under high pressure/temp with H2 and Ra-Ni.
  • Reduction affected by electron donating/withdrawing groups.

Carbonyl Chemistry

• Ketones and Aldehydes:

  • Hydrates, hemiacetals, acetals formation.
  • Reactions with amines: Imines and enamines formation.
  • Grignard and Wittig reactions for C-C bond formation.

• Carboxylic Acids:

  • Formation from alkyl bromides, Grignard reagents, oxidation.
  • Reduction to alcohols using LiAlH4.

Acid Derivatives

• Acid Chlorides:

  • Highly reactive, converted to carboxylic acids, esters, amides, ketones.
  • Reactions with organometallic compounds.

• Esters and Amides:

  • Esterification and amidation processes.
  • Fischer esterification for ester formation.

Organometallic Chemistry

• Formation of Organometallic Reagents:

  • Organolithium and Grignard reagents for nucleophilic addition.

• Suzuki Coupling:

  • Coupling boronates with alkyl halides to form C-C bonds.

Nitriles and Amines

• Nitriles:

  • Formation through SN2 reactions.
  • Hydrolysis to carboxylic acids.

• Amines:

  • Formation via reduction of nitriles, azides, and amides.
  • Gabriel synthesis for primary amines.

Enol and Enolate Chemistry

• Alpha Halogenation:

  • Addition of halogens to alpha carbon of carbonyls.

• Aldol Reactions:

  • Aldol addition and condensation for C-C bond formation.

• Michael Addition:

  • Addition of stabilized carbon nucleophiles to alpha-beta unsaturated carbonyls.

Sigmatropic Rearrangements

• Cope and Claisen Rearrangements:
  • Sigma bonds shift positions, reorganizing molecular structure.

Summary

• Mastery of these reactions allows for synthesis and transformation of a wide range of organic compounds.
• Practice problems and deeper dives into specific reactions recommended for comprehensive understanding.