A-Level Chemistry: Nomenclature of Organic Compounds

Jun 13, 2024

A-Level Chemistry: Nomenclature of Organic Compounds

Introduction

  • Topic: Nomenclature (naming of organic compounds).
  • Focus: Rules for naming using given formulas and drawing structures from names.
  • System Used: IUPAC (International Union of Pure and Applied Chemistry).
  • Specific coverage of families and functional groups relevant in Year 1 Chemistry.

Key Naming Rules

  • Root: Indicates the longest unbranched hydrocarbon chain.
    • Common roots: Meth (1), Eth (2), Prop (3), But (4), Pent (5), Hex (6).
    • Chain length longest in A Level: Maximum of 6 carbons.
  • Endings: Typically -ane (no double bonds) or -ene (double bonds present).
  • Suffixes: Change according to functional groups (e.g., -ol for alcohols).
  • Prefixes: Indicate branches or additional functional groups (e.g., methyl-).

Example Naming of Simple Compounds

  • Alkanes: 'Methane' (1 carbon, CH₄), 'Propane' (3 carbons, C₃H₈).
  • Alkenes: Numbers specify double bond positions (e.g., But-1-ene).

Branched Alkanes and Alkenes

  • Rules for Branches:
    • Identify the longest chain.
    • Name the branches (R groups): Methyl (1C), Ethyl (2C), etc.
    • Number the chain to give the lowest numbers for branches and double bonds.
  • Examples:
    • 2-methylpropane (CH₃-CH(CH₃)-CH₃).
    • 3-ethylpentane (CH₃-CH₂-CH(CH₂-CH₃)-CH₂-CH₃).

Functional Groups and Complex Naming

  • Haloalkanes: Prefix includes the halogen (Bromo-, Chloro-).
    • Examples: 1,2-dichloroethane (Cl-CH₂-CH₂-Cl).
  • Alcohols: Suffix -ol, position indicated by number.
    • Examples: Methanol (CH₃OH), Propan-2-ol (CH₃-CHOH-CH₃).
  • Aldehydes and Ketones: Suffix -al or -one.
    • Aldehyde example: Butanal (CH₃-CH₂-CH₂-CHO).
    • Ketone example: Pentan-2-one (CH₃-CO-CH₂-CH₂-CH₃).
  • Carboxylic Acids: Suffix -oic acid.
    • Examples: Ethanoic acid (CH₃COOH).
  • Amines: Suffix -amine, branches named as prefixes.
    • Examples: Methylamine (CH₃NH₂).
  • Nitriles: Suffix -nitrile.
    • Examples: Propanenitrile (CH₃CH₂CN).

Double Function Groups: Naming and Precedence

  • Order of Precedence:
    • Carboxylic acids > Nitriles > Aldehydes > Ketones > Alcohols > Amines.
  • Multiple Functional Groups:
    • Main group as suffix; others as prefixes (e.g., aminoethanoic acid).
    • Proper numbering ensures lowest combined numbers and correct ordering.

Special Cases: Dials, Dienes, and Dicarboxylic Acids

  • Dials (two alcohol groups): Names include -diol.
    • Example: Ethane-1,2-diol (HOCH₂-CH₂OH).
  • Dienes (two double bonds): Names include -diene.
    • Example: Buta-1,3-diene (CH₂=CH-CH=CH₂).
  • Dicarboxylic Acids: Names include -dioic acid.
    • Example: Propane-1,3-dioic acid (HOOC-CH₂-COOH).

Drawing Structures from Names

  • Key Points:
    • Identify root and functional groups.
    • Draw main chain and add groups based on numbering.
  • Practice Examples included in lecture.

Conclusion

  • Follow-up: Continued review of isomerism and naming in future videos.