Chemical Reactions of Alkanes

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Chemical Reactions of Alkanes

• 1. Combustion
• 2. Desaturation- forms alkenes
• 3. Halogenation- forms alkyl halides

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Chemical Reactions of Alkanes Combustion
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Chemical Reactions of Alkanes Desaturation-
forms alkenes
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Chemical Reactions of Alkanes Halogenation-
forms alkyl halides
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Mechanism of Halogenation is Free Radical Based
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2nd Step in Mechanism of Halogenation is
Elongation
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Various Combinations of Free Radicals Represent
Termination
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Nomenclature of Alkyl Halides

• 1. Chain as alkanes
• 2. -ine of halogen changed to -o
• Identify attachment site
• e.g. 2-chloroethane

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Physical Properties of Alkyl Halides

• 1. Polar
• 2. Liquid instead of gas
• 3. Tend to be toxic, taken internally

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Predominant Product

• Determined by radical stability
• Direction of stability

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Stereochemistry

• Chiral Carbon- a carbon which has four different
  groups bonded to it
• Dashed wedge behind solid wedge, in front
• Enantiomers- nonsuperimposable, mirror images

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The RS system of nomenclature

• 1. Position the molecule so the H is in back
• 2. Number highest mol. wt. (1) to lowest (3)
• 3. Clockwise R, counterclockwise S

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Alkenes Names and Structures

• Alkenes- hydrocarbons that have one or more
  double bonds between carbon atoms
• CnH2n
• Monounsaturated- one double bond
• Polyunsaturated- two or more double bonds

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Naming Alkenes

• 1. Find the longest continuous carbon chain that
  contains the double bond(s), even if it is not
  the longest carbon chain, and number from the end
  nearer the double bond.
• 2. Write the alkane name corresponding to the
  longest carbon chain, then change the -ane suffix
  to -ene.
• 3. Identify by number the lower-numbered carbon
  atom containing a double bond, followed by a
  hyphen directly before the alkene name precede
  this by naming substituents in the usual way.
• 4. If two or more double bonds occur, specify
  each double bond by number and use an appropriate
  prefix before -ene to indicate the number of
  double bonds.

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Cis-Trans Isomerism

• 1. R groups must be attached to different
  carbons
• 2. Larger R groups get priority

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Practice

• Give the IUPAC name for the above molecules

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More Practice

• Draw the structure of the following compounds,
  for which a correct IUPAC name is given
• cis-3-hexene
• 3-ethylcyclohexene

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Properties of Alkenes and Alkynes

• 1. nonpolar
• 2. less dense than alkanes
• 3. trend toward gas rather than liquid
• 4. used to make polymers

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Reactions of Alkenes

• Addition reaction- since H has been taken away to
  create a double bond, H or other molecules can be
  added across the double bond, yielding a
  substituted alkane.
• 1. catalytic hydrogenation
• 2. halogenation
• 3. addition of HCl and HBr (Markovnikonv's rule)
• 4. hydration
• 5. oxidation

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Reactions of Alkenes Catalytic Hydrogenation
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Reactions of Alkenes Halogenation
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Reactions of Alkenes Acid-Catalyzed Hydration
(Markovnikovs Rule)
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Reactions of Alkenes Addition of HCl and HBr
(Markovnikovs Rule)
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Reactions of Alkenes Catalytic Hydrogenation

• Addition reaction- since H has been taken away to
  create a double bond, H or other molecules can be
  added across the double bond, yielding a
  substituted alkane.
• 1. catalytic hydrogenation
• 2. halogenation
• 3. addition of HCl and HBr (Markovnikonv's rule)
• 4. hydration
• 5. Others exist

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Alkynes Names and Structures

• Alkynes- hydrocarbons that have one or more
  triple bonds between carbon atoms
• CnH2n-2
• Named as alkenes, with the exception that -yne is
  used instead of -ene

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Reactions of Alkynes

• Since H has been taken away to create the triple
  bond, just as for a double bond, the same
  reactions will occur for alkynes as alkenes.
• The difference is, 2 moles will be added instead
  of 1.