chem the names of organic compounds
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THE NAMES OF ORGANICCOMPOUNDS
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There are two skills you have todevelop in this area:
You need to be able to translate thename of an organic compound into its
structural formula. You need to be able to name a
compound from its given formula.
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Counting the carbon atoms
You will need to remember the codesfor the number of carbon atoms in achain up to 6 carbons. There is no
easy way around this - you have got tolearn them. If you don't do thisproperly, you won't be able to name
anything!
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code no of carbonsmeth 1eth 2
prop 3but 4
pent 5hex 6
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Types of carbon-carbon bonds
Whether or not the compoundcontains a carbon-carbon double bond
is shown by the two lettersimmediately after the code for thechain length.
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code meansan only carbon-carbon
single bondsen contains a carbon-
carbon double bond
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For example, butanemeans four
carbons in a chain with no doublebond.
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Propene means three carbons in
a chain with a double bondbetween two of the carbons.
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Alkyl groups Compounds like methane, CH4, and ethane,
CH3CH
3, are members of a family of compounds
called alkanes. If you remove a hydrogen atom
from one of these you get an alkyl group.
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For example:
A methyl group is CH3. An ethyl group is CH3CH2.
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Types of compounds
Example 1: Write the structural
formula for 2-methylpentane.
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Start decoding the name from
the bit that counts the number
of carbon atoms in the longestchain - pent counts 5 carbons.
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Now draw this carbon skeleton:
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Put a methyl group on thenumber 2 carbon atom:
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Does it matter which end you startcounting from? No - if you counted
from the other end, you would drawthe next structure. That's exactly thesame as the first one, except that it
has been flipped over.
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Finally, all you have to do is to put inthe correct number of hydrogen atomson each carbon so that each carbon is
forming four bonds.
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Write the structural formula for
2,3-dimethylbutane.
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Write the structural formula for 2,2-dimethylbutane.
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The cycloalkanes
In a cycloalkane the carbon atoms arejoined up in a ring - hence cyclo.
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Example: Write the structural
formula for cyclohexane.
hexanshows 6 carbons with no carbon-
carbon double bonds. cycloshows thatthey are in a ring. Drawing the ring andputting in the correct number of hydrogens
to satisfy the bonding requirements of thecarbons gives:
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The alkenes
Example 1: Write the structuralformula for propene.
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propcounts 3 carbon atoms in thelongest chain. entells you that there isa carbon-carbon double bond. Thatmeans that the carbon skeleton lookslike this:
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Putting in the hydrogens gives you:
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Write the structural formula for 3-methylhex-2-ene
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Adding the hydrogens gives the finalstructure:
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Be very careful to count the bondsaround each carbon atom when youput the hydrogens in. It would be very
easy this time to make the mistake ofwriting an H after the third carbon - butthat would give that carbon a total of 5
bonds.