CH 106 - Lesson 2
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Nomenclature

Carbon-to-carbon triple bonds in a compound means that a still different ending has to be used for the name. For a triple bond, we use a -yne ending. With the exception of the -yne ending, the same naming process is used as was used for alkenes.

Let's look at some examples of alkene nomenclature. (These are also shown in Example 11 in your workbook.) Again, let me emphasize that it is the same system that you have gone through before but with a differnet ending to represent a different functional group.
When two carbon atoms are present, we have an eth- prefix and a -yne ending to indicate a triple bond. This compound is named ethyne. Its common name is acetylene.

CH CH
ethyne (acetylene)
The alkyne with three carbon atoms is called propyne.


CH C - CH3

propyne
These three are 1-butyne, 2-butyne, and 1-butyne. Note that it is important to count carbon atoms from the end of the chain closest to the triple bond.
CH C - CH2 - CH3 1-butyne
CH3 - C C - CH3 2-butyne
CH3 - CH2 - C CH 1-butyne
Again, other functional groups can be added to chains which contain triple bonds, as shown in this compound, 3-chloro-4-methyl-1-pentyne.

CH3 - CH - CH - C CH
|      |  
CH3  Cl     
3-chloro-4-methyl-1-pentyne

 

Practice

Example 12 will give you some practice naming and drawing structural formulas for alkynes.

C - C - C C - C
C - C C - C - C - C
      |
      C
3,3-dimethyl-1-heptyne
2-methyl-5-ethyl-3-octyne

 

Answers

C - C - C C - C 2-pentyne
C - C C - C - C - C
      |
      C
4-methyl-2-hexyne
3,3-dimethyl-1-heptyne C          
|         
C C - C - C - C - C - C
|         
C
         
2-methyl-5-ethyl-3-octyne C - C - C C - C - C - C - C
|               |           
C              C - C
    

 

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