chem the names of organic compounds

8/2/2019 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.

chem the names of organic compounds

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