Reactions of the Alkanes
1.  Halogenation with light:
       This is a substitution reaction:

       R-H + halogen  -----------> R-F, R-Cl or R-Br        +      HF, HCl or HBr     (R can be any alkane)
                                    light
                    butane                                                                 chlorobutane



2.   Dehydrohalogenation:
This reaction is used to remove a hydrogen and a halogen from an alkane chain. The result is the formation of a double bond.  In the diagram below X can be any halogen.

KOH is strongly ionic and basic.  The K+ ion found in solution is strong enough to pull the F- ion away from the weaker covalent attachment on the carbon. This frees up one bonding electron on the carbon. The OH- ion attacks a H+ ion that is still attached to the carbon chain. It pulls it off forming water. The second bonding electron is now free. The two free bonding electrons join to form the second covalent or alkene (C=C) bond. If an alkene bond is already there then an alkyne (CC) bond will form.  If there are two halogens then both will be removed and an alkyne bond will also form.
    2-bromo-butane                                    but-1-ene              but-2-ene

The Br- gets pulled off by the K+. The H+ gets pulled off randomly f rom either side of the Br's position so there are two possible products. The alcohol in the reagent is needed to help dehydrate (suck up the water from the products.)

3o halides react better than 2o halides which react better than 1o halides.

          ie.          >         > 
          tert-butyl chloride          2-chloropropane               1-chloropropane



3.  Halocyano Substitution
This reaction removes a halogen from a haloalkane and adds a cyano group.  This can also increase the C chain length by one.

eg. iodo-pentane is converted to cyano-pentane



4.  Dehydration
      This reaction removes water from a molecule. It works great on alcohols.

Works best for 3o alcohols > 2o alcohols > 1o alcohols

eg.   iso-propyl alcohol being dehydrated into propene and water

.
The acid works by pulling off a H2O molecule from the organic molecule. Once formed the H2O stays in the acid because the acid is very hydrophilic (water loving). During dehydration and the formation of an alkene 2 products always form depending on the rotation around the original single bond.  When the hydroxyl group is in the middle of a odd numbered molecule the should be only one product.  Because of the double bond there is the possibility of getting cis, trans isomers forming.  If a diol is present both alcohols will be removed and an alkene bond will form.

        pentan-3-ol                                          cis-pent-2-ene          trans-pent-2-ene