IUPAC Nomenclature of Alkanes

Jun 4, 2024

IUPAC Nomenclature of Alkanes

Introduction to Nomenclature

  • Importance of standardized naming in organic chemistry
  • Transition from general chemistry notation to organic chemistry notation

Line Notation

  • Definition and purpose in organic chemistry
  • Every vertex and endpoint symbolizes a carbon atom
  • Hydrogens are implied, showing maximum number attached to carbons
  • Example: Five-carbon hydrocarbon shown as line notation

Tetrahedral Molecular Geometry

  • Alkanes have carbons with sp3 hybridization
  • Alkanes are fully saturated (no double/triple bonds)
  • Tetrahedral geometry: each carbon bonded to four atoms
  • Wedge and dash notation: Wedge = coming out of the plane, Dash = going into the plane

IUPAC Naming Rules

  • Need for universal naming conventions for clear communication
  • Rules developed by IUPAC (International Union of Pure and Applied Chemistry)

Alkanes

  • Definition: hydrocarbons containing only single bonds, fully saturated
  • Suffix: “-ane”
  • Prefix: Dependent on number of carbons in the molecule

Common Alkanes Prefixes

  • 1 carbon: Meth-
  • 2 carbons: Eth-
  • 3 carbons: Prop-
  • 4 carbons: But-
  • 5 carbons: Pent-
  • 6 carbons: Hex-
  • 7 carbons: Hept-
  • 8 carbons: Oct-
  • 9 carbons: Non-
  • 10 carbons: Dec-

Example: Pentane

  • Five-carbon alkane: Pentane (Pent- + -ane)

Branched-Chain Alkanes

Identifying the Longest Chain

  • Longest chain determines the base name of the molecule
  • Example: Four-carbon main chain with one-carbon substituent

Numbering the Chain

  • Number the chain in a direction that gives the substituent the lowest number
  • Example: Numbering left to right vs. right to left

Naming the Substituents

  • Use common prefixes with “-yl” suffix for substituents
  • Examples: Methyl (one-carbon substituent), Ethyl (two-carbon substituent), Propyl (three-carbon substituent)

Full Name Example

  • Identify the main chain: Butane (four carbons)
  • Identify substituent and its location: Methyl group on carbon 2
  • Full name: 2-methylbutane
  • Importance: Any chemist globally can unambiguously identify the molecule

Conclusion

  • Importance of these conventions for universal communication among chemists
  • Encouragement to subscribe and ask questions