C 10 J

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C 10 J

• Alkanes

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Lecture Outline

• Nomenclature of alkanes
• Nomenclature of alkenes
• The homologous series
• Constitutional Isomerism

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Alkanes

• Natural sources
• Petroleum
• Natural gas (methane ethane)

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Alkanes

• General formula CnH2n2
• A series of compounds in which the members are
  built up in a regular, repetitive way is called a
  homologous series.
• Similar chemical and physical properties

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NomenclatureIUPAC rules

• The ane ending is used for all saturated
  hydrocarbons
• Unbranched alkanes are named according to the
  number of carbon atoms in the compound

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Nomenclature contd

• For branched alkanes, the root name is that of
  the longest continuous chain of carbon atoms
• Groups attached to the main chain are termed
  substituents (e.g. alkyl groups)
• Alkyl groups are named by taking the name of the
  alkane and changing the ane to -yl

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Some common substituents
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Nomenclature contd

• The main chain is numbered so that the first
  substituent along the chain receives the lowest
  number
• The terms di, tri, tetra, penta etc. are used
  when two or more identical groups are attached to
  the main chain

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• IUPAC names for hydrocarbons are written as one
  word
• Numbers are separated from each other by commas
  and are separated from letters by hyphens
• There is no space between the last named
  substituent and the name of the parent alkane
  that follows it.

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• NOMENCLATURE QUIZ
• http//196.3.3.103/tutorials/Nomenclature/inde
  x.html

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Naming cyclic alkanes

• Cycloalkanes are saturated hydrocarbons that have
  at least one ring of carbon atoms
• General formula CnH2n
• They are named by placing the prefix cyclo before
  the alkane name corresponding to the number of
  carbon atoms in the ring

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Naming cyclic alkanes

• Alkyl or halogen substituents attached to the
  rings are named similarly to alkanes
• If there is only one substituent present, no
  number is required to locate it
• With several substituents, numbers are required
  to identify their positions

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Cyclic alkanes

• The ring carbons are numbered to give the
  substituents the lowest possible numbers
• One substituent is denoted carbon number 1
• With different substituents, the one with the
  highest alphabetic priority is located at carbon 1

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Representation of alkanes
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Representation of alkenes
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Representation of Alkynes
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Nomenclature in Alkenes

• The ending ene is used to designate the
  carbon-carbon double bond
• The longest chain containing both carbons of the
  double bond is selected as the parent structure
• For more than one double bond, the ending is
  diene, triene
• Compounds with a double and triple bond are
  -enynes

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Nomenclature in Alkenes contd

• The chain is numbered beginning at the end of the
  chain nearer the double bond to assign it the
  lowest possible number
• The number of the first atom of the double bond
  is used as the prefix
• The positions of substituents are indicated by
  the numbers of the carbon atom to which they are
  attached

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• If more than one double bond is present in the
  molecule, numbering begins from the end nearer to
  the first double bond.

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Naming Cyclic alkenes

• Cycloalkenes are designated in such a way as to
  assign
• the 1-and 2- positions to the carbon atoms of
  the double bond
• The lowest combination of numbers to substituents

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Homologous series- Differ by methylene
(CH2)groups
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Constitutional Isomers

• Constitutional isomers possess the same number of
  atoms but they differ in the connectivities of
  the atoms
• Differ in their structural formulas

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Isomerism (Structural/ constitutional isomers)

• Octane 18 isomers
• Draw the other 10 isomers

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Exam QuestionDecember 2003

• Provide IUPAC names for the following compounds.