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Carbon Chemistry  

 

Hydrocarbons are named for the number of carbon atoms and the type of bonds they contain.

Alkanes are open-chained hydrocarbons in which only single bonds are present. Alkenes have one pair of carbon atoms in each molecule that are connected by a double bond. Alkynes have one pair of carbons atoms connected by a triple bond.

 Prefix names used: 

1: meth-     methane
2: eth-        ethane
3: prop-      propane
4: but-        butane
5: pent-      pentane 
6: hex-        hexane
7: hept-       heptane 
8: oct-          octane 
9: non-       nonane
10: dec-      decane

 Organic compounds are defined simply as compounds of carbon. Compounds that have the same molecular composition but different structures are called isomers. This is because the atoms are arranged in different ways.

 The hydrocarbon heptane, for example, has the molecular formula C7H16. Heptane has nine isomers. The structural formula of two are shown in Figure 1. Normal heptane boils at 98° C. Notice that the carbon atoms in normal heptane form a straight chain. In isoheptane, however, the chain branches. Instead of seven carbons in a row, there are six. The seventh carbon branches off from the second carbon

Figure 1.

                                                                                     

       

       H  H  H  H  H  H  H
        |  |   |  |   |   |   |
   H -C- C- C- C- C- C-  C - H
        |   |  |   |   |   |   |
        H  H  H  H  H  H   H

 

             normal heptane

 

 

                           

                   H
                    |
                H-C-H

        H          |      H  H  H  H
         |          |      |   |  |   |

     H-C   -     C  -   C- C-C - C - H

         |          |       |  |  |    |

         H         H       H H  H  H

 

                  isoheptane                                        

 Now you are going to draw some isomers. Before you begin, here are some hints. When diagramming isomers, it's easier if you begin by linking the carbon atoms together. Then fill in the hydrogens. Remember that every carbon atom has 4 bonding sites. Each hydrogen has only one bonding site. Be careful you don't draw the same isomer twice. Sometimes two structural formula may look different, but are actually the same. Look at the two structural formulas of isoheptane on the blackboard. Each has the seventh carbon attached to the second carbon from the end of chain.

 1. Draw a third isomer of heptane. Start with a six-carbon chain. Make the seventh carbon branch off from the third carbon in the chain. Remember, you must end up with 7 carbons and 16 hydrogens.

2. Construct another heptane isomer. This time use a 5 carbon chain with a second 2 carbon chain attached to the third carbon.


3. There are five more heptane isomers. Draw at least two. Try to get all five. Use extra paper to draw these.

 

4. There are three isomers for the compound pentane. Start by drawing normal pentane. This is a straight chain.

 5. Draw the other two isomers of pentane. Make sure you don't draw the same structure twice.

 6. The compound nonane has the chemical formula C9H20. Draw at least four isomers of this compound. Begin by drawing the straight-chain isomer. Then try branching structures. See how many you can draw.

 Naming carbon compounds with functional groups

Functional groups often give compounds their properties.  Functional groups are parts of molecules that react in characteristic ways.  Each of the lines represent a pair of electrons shared between two atoms (single or double covalent bonds).

 

--N --H
     \
     H        amino group

 

--OH   hydroxy group  (alcohols)

--Cl     chloro group

   

      O
      | |
  -- C -- OH    carboxy group

  

      O
      | |
  --  N
         \
         O      nitro group

 

Compounds with functional groups are named after the hydrocarbons you would have if the functional group were replaced with a hydrogen.  The carbons are numbered from one end of the carbon chain to determine which carbon the functional group is attached to.  That number is used before the functional group.

 

     H    H   Cl   H   H
      |      |     |      |     |
H - C- C - C - C - C - H
      |     |      |      |     |
     H   H    H    H   H          3-chloropentane

 

Draw:

a) 1-aminopropane
b) 1-hydroxyethane
c) 2-carboxybutane
d) 1-chloro-4-nitrohexane


 

Page Last Updated: Friday March 02, 2007           Webmaster: Larry Jones                 Pickens County School District