Chemistry of Alkenes Ch 7

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Chemistry of Alkenes (Ch 7)

• the double bond prevents free
  rotation
• isomerism cis and trans
• nomenclature E and Z (3 or 4
  different substituents
• around the double bond)

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Nomenclature

• Select the longest chain and replace the suffix
  ane with ene
• Start numbering the chain at the end nearer to
  the double bond
• Designate the location of the double bond
• CH2CHCH2CH3
  CH3CHCHCH2CH2CH3
• 1-butene
  2-hexene
• (not 3-butene)
  (not 4-hexene)
• Indicate the location of substituents by the
  number of the C atoms
• CH3
  CH3 CH3
  CH3 CH3
• CH3CCHCH3 CH3CCHCHCH3
  CH3CHCHCH2C-CH3
• 
  
  
  CH3

1 2 3 4 1 2 3
4 5 1 2 3 4 5
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2-methyl-2-butene 2,4-dimethyl-2-hexene
2,5,5-trimethyl-2-hexene
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Nomenclature

• Number susbtituted cycloalkenes in the way that C
  atoms at the
• double bonds have 1 and 2 positions and
  that substituents have lower
• at the first point of difference
• 6. If an alcohol group is present give the
  lowest possible to it.

1-methylcyclopentene
3,5-dimethylcyclohexene (not 2-methylcyclopentene
not 4,6-dimethylcyclohexene)
CH3 CH3CCHCHCH3
OH
4-methyl-3-penten-2-ol
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7. Decide about cis and trans or E and Z
Two common names CH2CH-
vinyl CH2CHCH2- allyl
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E and Z
Z heavier groups on the same side
E heavier groups on the two
opposite sides
(Z)-2-bromo-1chloro-1fluoroethene
(E)-2-bromo-1chloro-1fluoroethene
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(E)-1-bromo-1-choro-1-pentene (E)-2-bromo-1-
chloro-1-iodo-1-butene (Z)-3,5-dimethyl-2-h
exene
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Evaluating alkene relative stability
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trans more stable than cis (release of steric
hindrance) By using either heat of combustion or
heat of hydrogenation It is possible to
demonstrate that The greater of R groups
to the double bond the greater is the alkene
stability Electron donating ability of
alkyl groups to satisfy the increased
electronegativity of sp2 C atoms
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Cycloalkenes
Always cis till cycloheptene
cis-cyclooctene
trans-cyclooctene