Cycloalkanes

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Cycloalkanes
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Cycloalkanes

• Compounds that contain rings of carbon atoms
• Have the general formula CnH2n
• Represented by polygons in skeletal drawings

cyclopropane cyclobutane cyclopentane
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Naming cycloalkanes

• Count the number of carbon atoms in the ring and
  the number in the largest substituent.
• If the number of carbon atoms in the ring is
  equal to or greater than the number in the
  largest substituent, the compound is named as
  alkyl-substituted cycloalkane.

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• Substituted cycloalkane

Cycloalkyl-substituted alkane
Methylcyclopentane
3 carbons 4 carbons
1-cyclopropylbutane
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• 2. For alkyl-substituted cycloalkanes, start at
  a point of attachment and number the substituents
  on the ring so as to arrive at the lowest sum.

• 2 1
• 3 6
• 4 5

• 6 1
• 5 2
• 4 3

1,3-dimethylcyclohexane NOT
1,5-dimethylcyclohexane
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• When two or more different alkyl groups or
  halogens are present, number them by alphabetical
  priority.

1-ethyl-2-methylcyclopentane NOT
2-ethyl-1-methylcyclopentane
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Cis-trans isomers

• Because there is not free rotation in
  cycloalkanes, geometric isomers called
  stereoisomers are formed.
• Cis (L. on the same side)
• Trans (L. across from)
• Geometric isomers do not convert back and forth.

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trans-1,4-dichlorocyclohexane
cis-1,4-dichlorocyclohexane
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Chair Conformation
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Homework

• Page 320 39-43