Structure of aliphatic hydrocarbons

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Structure of aliphatic hydrocarbons
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Aliphatic hydrocarbons

• Aliphatic hydrocarbons are hydrocarbons that
  consist of straight or branched chains of carbon
  atoms, or rings of carbon atoms other than those
  containing a special ring called a benzene ring

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Pentane a straight chain aliphatic hydrocarbon
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A branched chain hydrocarbon
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Cyclohexane a cyclic aliphatic hydrocarbon
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Homologous series

• A homologous series is a family of organic
  compounds with the same general formula, similar
  chemical properties, and successive members
  differing by CH2
• Alkanes, alkenes and alkynes are three different
  homologous series of aliphatic hydrocarbons

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Alkanes

• Alkanes are a homologous series of hydrocarbons
  with the general formula CnH2n2
• They are named systematically, with a prefix
  indicating the number of carbon atoms per
  molecule, and the ending ane

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Alkanes

• Methane CH4
• Ethane C2H6
• Propane C3H8
• Butane C4H10

• Pentane C5H12
• Hexane C6H14
• Heptane C7H16
• Octane C8H18

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Alkanes

• Alkane molecules are tetrahedral, e.g. propane

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Structural formulas

• The structural formula of an alkane indicates the
  way atoms in a molecule of the alkane are bonded
  together
• The following slides show the structural formulas
  of some of the alkanes

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Methane
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Ethane
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Propane
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Butane
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Pentane
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Structural isomers

• Structural isomers are compounds that have the
  same molecular formula but different structural
  formulas
• Butane (C4H10)is the simplest alkane which has
  structural isomers, called butane and
  2-methylpropane respectively
• The name 2-methylpropane indicates that there is
  a methyl (CH3) group attached instead of one of
  the hydrogen atoms to the second carbon in propane

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Isomers of butane
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An isomer of octane (C8H18)

• 2,2,4-trimethylpentane is so called because there
  are two methyl groups attached (in place of
  hydrogen atoms) to the second carbon atom and one
  (in place of another hydrogen atom) to the fourth
  carbon atom in a pentane molecule

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Physical properties of alkanes

• Physical state The first four alkanes are gases,
  while pentane and higher alkanes are liquids
• Insoluble in water
• Soluble in non-polar solvents such as cyclohexane

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Alkenes

• Alkenes are a homologous series of hydrocarbons
  with the general formula CnH2n
• They are named systematically, with a prefix
  indicating the number of carbon atoms per
  molecule, and the ending ene

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Alkenes

• Ethene C2H4
• Propene C3H6
• But-1-ene C4H8
• But-2-ene C4H8

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Ethene
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Propene
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But-1-ene
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But-2-ene
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Physical properties of alkenes

• Physical state Gases
• Insoluble in water
• Soluble in non-polar solvents such as cyclohexane

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Alkynes

• Alkynes are a homologous series of hydrocarbons
  with the general formula CnH2n-2
• Ethyne (C2H2) is the first member of the series

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Physical properties of ethyne

• Physical state Gas
• Insoluble in water
• Soluble in non-polar solvents such as cyclohexane