4.3.2

Functional Groups

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Homologous Series

A homologous series is a set of compounds with the same functional group. Members of a homologous series have very similar properties because they have the same functional group.

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General formulae

  • Every homologous series has its own general formula:
    • E.g. Alkanes: CnH2n+2
    • E.g. Alkenes: CnH2n
    • E.g. Alcohols: CnH2n+2O
  • The general formula gives the molecular formula for each compound in the homologous series.
  • Different molecules in the series differ mainly in the length of their aliphatic chains.
    • Aliphatic chains are carbon chains that do not have a benzene ring.
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Functional groups

  • A functional group is a group of atoms that characterise the chemistry of a molecule. Functional groups cause specific reactions to happen with certain reagents.
  • Examples of functional groups are:
    • Hydroxyl group (-OH).
    • Carboxylic acid group (-COOH) (pictured).
    • Carbon-carbon double bond (C=C).
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Alkyl group

  • An alkyl group is a saturated hydrocarbon chain attached to a molecule.
    • The letter R can be used to represent alkyl groups.
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Aliphatic

  • Aliphatic compounds contain carbon chains that do not involve a benzene ring.
  • Aliphatic chains can be saturated, unsaturated, straight, branched or circular.
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Alicyclic

  • Alicyclic compounds are aliphatic compounds that have non-aromatic rings but no side chains.
    • E.g. Cyclohexane.
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Aromatic

  • Aromatic compounds contain at least one benzene ring.
  • Benzene rings tend to make these compounds smell.
    • This is why these compounds are described as aromatic.
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Saturated/unsaturated

  • Saturated compounds contain single bonds only between carbon atoms (C-C).
  • Unsaturated compounds contain at least one different carbon-carbon bond such as C=C or an aromatic ring.

Jump to other topics

1Principles of Science I

1.1Structure & Bonding

1.2Properties of Substances

1.3Cell Structure & Function

1.4Cell Specialisation

1.5Tissue Structure & Function

1.6Working with Waves

1.7Waves in Communication

2Practical Scientific Procedures and Techniques

3Science Investigation Skills

4Principles of Science II

4.1Extracting Elements

4.2Relating Properties to use of Substances

4.3Organic Chemistry

4.4Energy Changes in Industry

4.5The Circulatory System

4.6Ventilation & Gas Exchange

4.7Urinary System

4.8Cell Transport

4.9Thermal Physics

4.10Materials

4.11Fluids

5Contemporary Issues in Science

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