Lecture Notes: Naming Organic Molecules

Introduction

• Understanding basic organic chemistry nomenclature is essential.
• Key terms:
  • Hydrocarbon: a chain of hydrogen and carbon.
  • Alkanes: all single bonds.
  • Alkenes: contain at least one double bond.
  • Alkynes: contain at least one triple bond.

Naming Hydrocarbons

1. Identify the Longest Carbon Chain: This determines the base name.
2. Check for Double/Triple Bonds: Change the suffix based on bonds (ane, ene, yne).
3. Identify and Number Branches: Number to give lowest numbers to branches or bonds.
   • Carbons make four bonds; add hydrogens to satisfy this.

Alkanes

• Formula: CₙH₂ₙ₊₂ (e.g., C₆H₁₄ for six carbons).
• Prefixes for chain length (1-10 carbons):
  • Meth-, Eth-, Prop-, But-, Pent-, Hex-, Hept-, Oct-, Non-, Dec-.
• Example:
  • Butane: 4 carbons with single bonds.
  • 1-Butene: 4 carbons, double bond starts at carbon 1.
  • Ethyne: 2 carbons with a triple bond.

Branches and Substituents

• Naming Branches:
  • End with "-yl" (e.g., Methyl, Ethyl).
  • Number position if necessary.
• Example: 2-Methylpropane

Halogen Substituents

• Halogens replace a hydrogen.
• Naming: replace "-ine" with "-o" (e.g., Fluoro, Chloro).
• Examples:
  • 1-Fluoropropane
  • 2-Chlorobutane

Multiple Substituents

• Use prefixes like "di", "tri" for multiple similar groups (e.g., 2,3-Dichlorobutane).

Cyclic Compounds

• Cycloalkanes are cyclic versions of alkanes.
  • Prefix "cyclo-" (e.g., Cyclopentane, Cyclohexane).
• Cyclohexane can form chair and boat conformations.

Aromatic Compounds

• Aromatics have delocalized electrons forming stable rings (e.g., Benzene).
• Double bonds in aromatics are less reactive and the same length as single bonds.
• Substituents: prefix (e.g., Fluorobenzene, Chlorobenzene).

Practical Application

• Focus on carbon when naming, not hydrogens.
• Add hydrogens to satisfy each carbon's 4-bond requirement.
• Practice with examples (e.g., drawing 3-Ethylpentane).

Conclusion

• Practice naming using the rules discussed.
• Questions can be directed to the instructor for clarification.