Hydrocarbons Lecture Notes

Introduction to Hydrocarbons

• Definition: Molecules containing only carbon and hydrogen.
• Examples:
  • Methane (CH₄)
  • Ethane (C₂H₆)

Types of Hydrocarbons

Aliphatic Hydrocarbons

• Includes:
  • Alkanes
  • Alkenes (contain carbon-carbon double bonds)
  • Alkynes

Aromatic Hydrocarbons

• Example: Benzene ring (C₆H₆)
  • Contains alternating double bonds in a cyclohexane ring (also known as an arine)

Saturated vs. Unsaturated Hydrocarbons

• Saturated Hydrocarbons:
  • Alkanes are saturated (CₙH₂ₙ₊₂)
  • Contains only single bonds (sigma bonds)
  • Maximum number of hydrogen atoms per carbon atom
• Unsaturated Hydrocarbons:
  • Includes alkenes, alkynes, and aromatic rings
  • Contains double bonds (pi bonds)
  • Examples:
    • Alkenes (CₙH₂ₙ)
    • Alkynes (CₙH₂ₙ₋₂)
    • Benzene (C₆H₆)

Alkanes (Saturated Hydrocarbons)

• General formula: CₙH₂ₙ₊₂
• First 10 alkanes:
  • C₁H₄: Methane
  • C₂H₆: Ethane
  • C₃H₈: Propane
  • C₄H₁₀: Butane
  • C₅H₁₂: Pentane
  • C₆H₁₄: Hexane
  • C₇H₁₆: Heptane
  • C₈H₁₈: Octane
  • C₉H₂₀: Nonane
  • C₁₀H₂₂: Decane
• First 20 alkanes:
  • C₁₁H₂₄: Undecane
  • C₁₂H₂₆: Dodecane
  • C₁₃H₂₈: Tridecane
  • C₁₄H₃₀: Tetradecane
  • C₁₅H₃₂: Pentadecane
  • C₁₆H₃₄: Hexadecane
  • C₁₇H₃₆: Heptadecane
  • C₁₈H₃₈: Octadecane
  • C₁₉H₄₀: Nonadecane
  • C₂₀H₄₂: Icosane

Alkenes

• General formula: CₙH₂ₙ (for one double bond)
• For each double bond, decrease hydrogen count by 2:
  • Example: 2-butene (C₄H₈)
  • Isomers:
    • Cis: Methyl groups on the same side
    • Trans: Methyl groups on opposite sides

Cycloalkanes

• Formula: CₙH₂ₙ (for one ring)
• For two rings: CₙH₂ₙ₋₂
• Example: Cyclopentane (C₅H₁₀)

Comparison of Alkanes and Cycloalkanes

• Pentane (C₅H₁₂) vs. Cyclopentane (C₅H₁₀)
  • Alkanes have maximum hydrogen atoms (saturated)
  • Rings or double bonds reduce hydrogen count

Alkynes

• General formula: CₙH₂ₙ₋₂ (for one triple bond)
• For each triple bond, decrease hydrogen count by 4:
  • Example: Acetylene (C₂H₂) vs. Ethane (C₂H₆)
  • Example: 2-butyne (C₄H₆) vs. Butane (C₄H₁₀)

Conclusion

• Hydrocarbons are essential organic molecules consisting solely of carbon and hydrogen.