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Understanding Alkanes and Their Nomenclature

Jan 27, 2025

Introduction to Alkanes and Nomenclature

Overview

  • Focus on alkanes and their nomenclature
  • Physical properties are covered in the textbook
  • Alkanes: Hydrocarbons with all carbon-carbon single bonds

Definition of Alkanes

  • Alkanes: Compounds with single carbon-carbon bonds
  • Can include functionalized alkanes with other types of double bonds (e.g., carbon-oxygen)

Structural and Conformational Isomerism

  • Free rotation around single (sigma) bonds allows different conformations
  • Introduction to Newman projections (future topic)

Naming Alkanes (Nomenclature)

Steps in Nomenclature

  1. Count the Carbons

    • Identify the longest carbon chain

  2. Prefix for Carbon Count

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

  3. Suffix Based on Bonds

    • Single bonds: -ane (Alkanes)

  4. Add Substituents

    • Groups attached to the main chain
    • Use suffix -yl for substituents

Examples

  • Butane and Butanal
  • Hexane: 6 carbons with single bonds
  • Octane: 8 carbons with single bonds

Substituents

  • Methyl (CH₃-)

    • Named by position: e.g., 3-methylpentane

  • Ethyl (Câ‚‚Hâ‚…-)

    • Use di-, tri-, tetra- for multiple groups: e.g., 4,5-diethyl-octane

Order of Naming

  • Alphabetical order for naming substituents
  • Numeric order for lowest possible numbers

Complex Molecules

  • Combine different substituents and numbers
  • E.g., 4-ethyl-5-methyl-octane

Special Names for Some Groups

  • Isopropyl: Connected off middle carbon
  • Sec-butyl: Off the second carbon of a butyl group
  • Tert-butyl: T-shaped arrangement

Incorporating Halides

  • Fluoro, Chloro, Bromo, Iodo
  • Use prefixes: 1-bromo, 3-chloro, 2-iodo-butane

Cycloalkanes

  • Ring structures
  • Naming similar to linear alkanes, but with "cyclo-"
  • E.g., Cyclohexane, Cyclopropane

Substituents on Cycloalkanes

  • Prioritize lowest numbering for substituents
  • E.g., 1-ethyl-2-methyl-4,4-dichloro-cyclohexane

Practice and Further Learning

  • Practice naming alkanes using examples
  • Refer to textbook and online resources for exercises
  • Contact instructor for help via email, office hours, or discussion sections

Conclusion

  • Understanding the fundamentals of alkane nomenclature is crucial for progressing in organic chemistry.

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