Introduction to Acids and Bases in Organic Chemistry

Key Concepts

• Acid Identification:
  • Acids typically contain hydrogen.
  • Examples: Hydrofluoric acid (HF), Hydrochloric acid (HCl), Ammonium ion (NH4+), Hydronium ion (H3O+), Acetic acid.
• Base Identification:
  • Common bases include Hydroxide, Fluoride, Ammonium, and conjugate bases of carboxylic acids.

pH Values

• Acids in water: pH < 7
• Bases in water: pH > 7
• Neutral water: pH ≈ 7

Acid-Base Reactions

• Bronsted-Lowry Definition:
  • Acids are proton (H+) donors.
  • Bases are proton acceptors.
• Example Reaction:
  • HF in water: HF (acid) donates H+ to water (base), forming Fluoride ion (F-) and Hydronium ion (H3O+).
• Reversibility:
  • Weak acids (like HF) do not completely ionize; reactions are reversible.

Conjugate Acids and Bases

• Hydronium (H3O+) is the conjugate acid of water.
• Fluoride (F-) is the conjugate base of HF.
• Conjugate Formulas:
  • Conjugate acid: Add H+
  • Conjugate base: Remove H+

Curve-Arrow Notation

• Mechanism Representation:
  • Arrows denote electron flow.
  • Full arrow: two electrons; Half arrow: one electron.

Additional Reactions

• Ammonia and Water:
  • Ammonia (NH3) acts as a base, water (H2O) as an acid.
  • Ammonia gains H+ to become Ammonium (NH4+), water becomes Hydroxide (OH-).

Acid Strength (Ka and pKa)

• Ka: Acid dissociation constant; larger value = stronger acid.
• pKa: Negative log of Ka; smaller value = stronger acid.
  • Strong acids have large Ka, small pKa.
• Comparisons:
  • HCl (strong acid) vs. HF (weak acid), based on pKa values.
  • Acetic acid vs. Hydrofluoric acid, based on Ka values.

Practice Examples

• Conjugate Forms:
  • Water: Conjugate acid H3O+, Conjugate base OH-.
  • Ammonia: Conjugate acid NH4+, Conjugate base NH2-.
  • Hydrogen sulfate: Conjugate acid H2SO4, Conjugate base SO4^2-.

Lewis Acids and Bases

• Definitions:
  • Lewis acid: Electron pair acceptor.
  • Lewis base: Electron pair donor.
• Examples:
  • Lewis acid: AlCl3, BH3.
  • Lewis base: NH3, F-.

Electrophiles and Nucleophiles

• Electrophiles: Electron poor, accept electrons.
• Nucleophiles: Electron rich, donate electrons.

Lewis Acid-Base Reactions

• Example: AlCl3 with NH3.
  • Ammonia donates lone pair to aluminum.
• Formal Charge Calculation:
  • Formula: Valence electrons - bonds - dots.

Reactivity and Stability

• Reaction Direction:
  • Reactions favor stability; shift towards weaker acid (higher pKa).
• Product vs Reactant Favored:
  • Use pKa values to determine direction of equilibrium.

This summary provided a basic overview of acids and bases, their reactions, and properties in the context of organic chemistry. Understanding these principles is key to mastering more complex organic reactions.