Hydrocarbons: open-chain alkanes

Open-chain alkanes.

OCR Salters B F331

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Open-chain alkanes

  • Have the general formula CnH2n+2
  • Name ends in -ane
  • Are saturated - all the bonds between carbon atoms are single bonds
  • Are aliphatic - they have no ring structures
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Naming alkanes

  • Choose the longest carbon chain and name it
  • Use prefixes in alphabetical order for any alkyl side chains
  • Use di, tri and tetra before the prefix if the side chains are identical
  • Show the position of any side chains by using numbers which are as low as possible, e.g. 2-methylbutane rather than 3-methylbutane
  • Put a comma between numbers and a hyphen between a number and a letter, e.g. 2,2-dimethylhexane
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Alkane names

The prefixes used in the alkanes are also used in naming other organic chemical compounds, so it is important for them to be learnt.

  • Methane - CH4
  • Ethane - C2H6
  • Propane - C3H8
  • Butane - C4H10
  • Pentane - C5H12
  • Hexane - C6H14
  • Heptane - C7H16
  • Octane - C8H18
  • Nonane - C9H20
  • Decane - C10H22
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Burning alkanes

  • Alkanes react completely with oxygen to produce carbon dioxide and water. This is called complete combustion.

C3H8 + 5O2  ->  3CO2 +4H2O

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Other reactions

  • Alkanes also undergo radical substitution reactions. (This is covered in Chemical Ideas 6.3 and Chemical Storylines A4)
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