Chemistry Day 4

Resonance Forms

• Definition and Stability

  • Resonance forms are different ways of drawing the structure of a molecule that can provide insight on its reactivity and stability.

  • Usually, one resonance form represents the most stable configuration.

• Acylium Ion Example

  • The acylium ion has multiple resonance structures; the one on the right is more stable due to fewer formal charges and less electronic repulsion.

Fundamental Reactions in Organic Chemistry

• Overview of Reactions

  • Five fundamental reactions in electrophilic aromatic substitution have been covered.

  • Introduction to new types of reactions, often involving single electron movement and radical chemistry from Organic Chemistry 1 (Ochem 1).

  • Emphasis on understanding reagents and products rather than detailed mechanisms.

• Benzylic Oxidation

  • Conversion of benzylic sites to carboxylic acids.

  • Requires oxidation steps, utilizing potassium permanganate (KMnO4) with water and hydrochloric acid (HCl).

  • An alternative involves chromium-based reagents (sodium or potassium dichromate).

• Conditions for Benzylic Oxidation

  • At least one C-H bond is required at the benzylic position for the reaction to proceed.

Reduction Reactions

• Alkenes to Alkanes & Nitro Reduction

  • Conditions to reduce alkenes can also reduce natural groups to amines.

  • Example of conditions: Iron or tin with HCl followed by sodium hydroxide (NaOH).

• Specific Reductions

  • Clemensen and Wolff-Kishner reductions target specific functional groups:

    • Nitro Reduction

      • Focused on converting nitro groups to amines.

    • Clemensen Reduction

      • Reduces ketones to alkanes while also affecting aldehydes.

  • The Wolff-Kishner reduction specifically acts on ketones.

Inductive and Resonance Effects

• Inductive Effect

  • Describes the electron-withdrawing or electron-donating ability based on electronegativity differences.

  • Relates to spatial geometry of molecules and dipoles.

• Resonance Effect

  • Focuses on electron density movement into or away from aromatic rings due to substituents.

  • Evaluating how lone pairs or pi bonds affect the ring's electron richness.

Free Energy Diagrams

• Understanding Reactivity

  • Creating free energy diagrams that reflect changes when substituents are added to a benzene ring.

  • Electron-withdrawing groups can lower the energy of the transition state in subsequent reactions.