Chapter 3 Alkanes

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Chapter 3 Alkanes
Important topics

• Nomenclature
• Properties and use of alkanes
• Conformation of alkanes
• ethane - the rotational barrier about a single
  bond
• butane - key conformers, energy diagrams
• Newman projection
• Cyclic alkanes
• ring strain
• conformers
• cis-trans isomers
• substituted cyclicohexanes
• Reactions

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Hydrocarbons
Alkanes

• All C-C single bonds
• Saturated with hydrogens
• Ratio CnH2n2

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IUPAC NamesRules that you need to remember

• Find the longest continuous carbon chain, and
  this defines the name of the alkane.
• Number the carbons, starting closest to the first
  branch, i.e., substituent.
• Name the groups attached to the chain, using the
  carbon number as the locator.
• Arrange substituents alphabetically.
• Use di-, tri-, etc., for 2, 3, etc., or multiples
  of same substituent.
  

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Longest Chain

• If there are two possible chains with the same
  number of carbons, use the chain with the most
  substituents.

Number the Carbon Chain

• Start at the end closest to the first attached
  group.
• If two substituents are equidistant, look for the
  next closest group.

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Name Alkyl Groups

• CH3-, methyl
• CH3CH2-, ethyl
• CH3CH2CH2-, n-propyl
• CH3CH2CH2CH2-, n-butyl

normal Alkyl group
Unfortunately, you must memorize these special
names.
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Propyl Groups
A secondary carbon

Butyl Groups
H
H
H
n-propyl
isopropyl
n-butyl
A primary carbon
H
sec-butyl
H
H
isobutyl
tert-butyl
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Alphabetize
3-ethyl-2,6-dimethylheptane

• Alphabetize substituents by name.
• Ignore di-, tri-, etc. for alphabetizing.

1-methyl-3-(1,2-dimethylpropyl)cyclohexane
Complex Substituents

• If the branch has a branch, number the carbons
  from the point of attachment.
• Name the branch off the branch using a locator
  number.
• Parentheses are used around the complex branch
  name.

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Physical Properties

• Solubility hydrophobic
• Density less than 1 g/mL
• Boiling points increase with increasing carbons
  (little less for branched chains).

Branched Alkanes

• Lower b.p. with increased branching
• Higher m.p. with increased branching
• Examples

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Boiling Points of Alkanes
Branched alkanes have less surface area
contact, so weaker intermolecular forces.
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Melting Points of Alkanes
Branched alkanes pack more efficiently into a
crystalline structure, so have higher m.p.
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Major Uses of Alkanes

• C1-C2 gases (natural gas)
• C3-C4 liquified petroleum (LPG)
• C5-C8 gasoline
• C9-C16 diesel, kerosene, jet fuel
• C17-up lubricating oils, heating oil
• Origin petroleum refining
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