Drawing and Naming Organic Molecules

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Drawing and Naming Organic Molecules

• Chapter 20. Sections 20.3-20.4

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Review

• What is the difference between something that is
  organic versus something that is inorganic?
• Why can carbon form so many molecules?
• What would be the formula for an alkane with 10
  carbons?
• What are isomers?

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Drawing structural isomers

• When you asked to draw isomers of an alkane this
  is how it works!
• Draw isomers of pentane- a 5 carbon alkane
• C5H12
• First draw the straight chain alkane.
• Then add the hydrogens
• We can represent this as CH3-CH2-CH2-CH2-CH3
• or CH3-(CH2)3-CH3

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Drawing structural isomers cont

• Now we draw an isomer of the straight chain
• It is easiest to remove a carbon from the end and
  bond it to the second carbon in the chain
• Now simply put in the hydrogens so that every
  carbon has four bonds.
• This can be represented as

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Drawing structural isomers cont

• We can also take two carbons out of the chain as
  well.
• Add in the hydrogens
• This can be represented as
• In fact many others would work as well

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Naming Alkanes

• Because there a millions and millions of organic
  compounds, there is a system to naming them, just
  as there is for naming inorganic compounds
• We will apply these rules to alkanes
• All alkanes have the root ane
• We then add a suffix to that root
• The first four are methane, ethane, propane,
  butane.
• After that they follow the Greek suffixes
• 5- pent
• 6-hex
• 7-hept
• 8-oct
• 9-non
• 10-dec

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Naming Alkanes cont

• So if you had a alkane with 8 carbons- it would
  be octane
• What about an alkane with 6 carbons?
• Hexane

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Naming Alkanes cont

• If you have a branched hydrocarbon- you go by the
  amount of carbons in the longest continuous chain
• Example
• So count the carbons- this will be a pentane

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Naming Alkanes cont

• When there is a non-hydrogen group attached to a
  chain- you need to identify it
• Example
• CH3 is a methyl group
• There are other groups
• -CH2CH3 ethyl
• -CH2CH2CH3- propyl
• There is a list on page 642 of your book

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Naming Alkanes cont

• Then you need to determine where the non-hydrogen
  group is added
• Count from the end closest to the branch to the
  end furthest away
• This is on the 3rd carbon

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Naming Alkanes cont

• If the substituent occurs more than once you need
  to indicate this by a using a prefix
• This is two methyls on the 2nd carbon of butane
  so it is 2,2 dimethylbutane

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Naming Alkanes RULES

• Find the longest continuous chain of carbon
  atoms- this determines the base name
• Number the carbons in the base chain, starting
  with the end closed to any branching (the first
  substituent)
• Use the appropriate name of an alkyl group,
  specify its position on the base chain with a
  number
• When a given type of alkyl group occurs more than
  once, attach the appropriate prefix
• Alkyl groups are always listed in alphabetical
  order (disregarding prefix)

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Naming Alkanes cont
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Naming Alkanes cont
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Naming Alkanes cont
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Naming Alkanes cont
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Naming Alkanes cont
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Naming Alkanes cont
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Homework

• Read page 639-648. Problems 1-5 on 648