Lecture Notes: IUPAC Nomenclature of Alkanes

Introduction

• Importance: Understanding nomenclature is crucial for discussing and referring to molecules by name in organic chemistry.
• Transition from General Chemistry: Move from using condensed formula notation to line notation in organic chemistry.

Line Notation

• Definition: Every vertex and endpoint is a carbon atom; hydrogens are implied.
• Example: Five-carbon hydrocarbon notation.
  • Vertices represent carbon atoms.
  • Maximum hydrogens implied at each carbon.
• Molecular Geometry:
  • Based on sp3 hybridization; carbon must bond with four different atoms.
  • Tetrahedral geometry visualized with wedge-dash notation.

IUPAC Nomenclature

• Purpose: Universal naming system agreed upon worldwide.
• Organization: IUPAC (International Union of Pure and Applied Chemistry) establishes rules.

Alkanes

• Definition: Hydrocarbons consisting only of carbon and hydrogen.
• Saturation: Fully saturated; maximum hydrogens, only single C-C bonds.
• Suffix: "ane" for alkanes.

Naming Alkanes

• Prefixes: Based on carbon count (meth, eth, prop, but, pent, hex, hept, oct, non, dec).
• Example:
  • Five-carbon alkane: Pentane.

Branched-Chain Alkanes

• Identifying Main Chain:
  • Find longest chain of carbons.
  • Example: Four-carbon main chain with one-carbon substituent.
• Numbering the Chain:
  • Number to give substituents the smallest possible number.
  • Example: Left-to-right numbering for earlier substituent occurrence.

Naming Substituents

• Rule: Use same prefixes, different suffix for substituents (e.g., methyl from methane but as substituent).
• Example:
  • One-carbon substituent is methyl.
  • Two-carbon substituent is ethyl.

Example Molecule

• 2-Methylbutane
  • Main chain: Butane (four carbons).
  • Substituent: Methyl group on carbon 2.
  • Naming: "2-methylbutane" universally indicates the structure.

Conclusion

• Naming conventions allow chemists worldwide to communicate molecule structure unambiguously.
• Encouragement to subscribe and ask questions for further learning.