Organic Chemistry Lecture Notes

Overview of Organic Chemistry

• Focus: Organic compounds containing carbon atoms.
• Importance of understanding bonding preferences for elements:
  • Hydrogen (H): 1 bond
  • Beryllium (Be): 2 bonds
  • Boron (B): 3 bonds
  • Carbon (C): 4 bonds
  • Nitrogen (N): 3 bonds
  • Oxygen (O): 2 bonds
  • Halogens (F, Cl, Br, I): 1 bond

Lewis Structures

• Example: Water (H2O)

  • Oxygen forms 2 bonds, each H forms 1 bond.
  • Total electrons around O: 8 (4 from bonds, 4 from lone pairs).

• Hydrogen Bond: Type of covalent bond when H is attached to N, O, or F.

  • Explains water’s high boiling point.

• Example: Methyl Fluoride (CH3F)

  • Carbon in the center, 4 bonds total (3 H, 1 F).
  • Fluorine has 3 lone pairs to achieve octet.

Bond Polarity

• Polar Bonds: Significant electronegativity difference (e.g., C-F is polar).
• Nonpolar Bonds: Electronegativity difference less than 0.5 (e.g., C-H is nonpolar).
• Charge Separation: Polarized molecules have positive and negative regions.

Types of Bonds

1. Covalent Bonds:
   • Nonpolar: Equal sharing of electrons (e.g., H2).
   • Polar: Unequal sharing (e.g., HF).
2. Ionic Bonds:
   • Electrons transferred between metals and nonmetals (e.g., NaCl).
   • Sodium becomes a cation (Na+), Chlorine becomes an anion (Cl-).
   • Electrostatic attraction holds ions together.

Overview of Alkanes

• General Formula for Alkanes: CnH2n+2
• Common Alkanes:
  • Methane (CH4)
  • Ethane (C2H6)
  • Propane (C3H8)
  • Butane (C4H10)
  • Pentane (C5H12)
  • Hexane (C6H14)
  • Heptane (C7H16)
  • Octane (C8H18)
  • Nonane (C9H20)
  • Decane (C10H22)

Drawing Lewis Structures of Alkenes and Alkynes

• Alkenes (C2H4):
  • Double bond between carbons.
  • Known as ethene.
• Alkynes (C2H2):
  • Triple bond between carbons.
  • Known as ethyne (acetylene).

Bond Length and Strength

• Bond Length:

  • Single bond > Double bond > Triple bond.
  • Example lengths:
    • C-C single bond: 154 pm
    • C=C double bond: 133 pm
    • C≡C triple bond: 120 pm

• Bond Strength:

  • Single bond < Double bond < Triple bond.
  • Sigma bonds (σ) are stronger than pi bonds (π).

Hybridization

• Determine hybridization by counting groups around carbon:
  • sp3: 4 groups
  • sp2: 3 groups
  • sp: 2 groups

Formal Charge Calculation

• Formula: Formal Charge = Valence Electrons - (Bonds + Lone Pairs)
• Examples:
  • Carbon: 4 valence electrons; calculate based on bonds and lone pairs.
  • Sulfur: 6 valence electrons.
  • Nitrogen: 5 valence electrons.

Functional Groups in Organic Chemistry

• Alcohols: Contain OH group (e.g., Ethanol).
• Aldehydes: Contain carbonyl (C=O) group at chain end (e.g., Acetaldehyde).
• Ethers: Oxygen between two carbons (e.g., Dimethyl Ether).
• Ketones: Carbonyl group in the middle (e.g., Propanone).
• Esters: Combination of carbonyl and ether functional groups.
• Carboxylic Acids: Contain carbonyl and hydroxyl groups (e.g., Pentanoic Acid).

Summary of Key Points

• Understand bonding preferences, types of bonds, and functional groups in organic chemistry.
• Importance of being able to draw and interpret Lewis structures.