Organic Chemistry Naming: Part 1 of Many

Alkanes

You may be unaware that you use alkanes all the time.  Some examples are the the fuels you use everyday.

This is propane and methane(being released).

Alkanes serve many purposes.  They can be used as a plant hormone, in the production of polymers, and in components of gasoline.  

Alkanes are also saturated hydrocarbons(compounds containing only Carbon and Hydrogen).  You can easily remember this because the prefix "hydro" means water(even though the compound has no Oxygen there are still Hyrogen atoms).  Seeing that the word carbon is already in the word, it doesn't get any more obvious.  Saturated means that the molecule contains the maximum number of hydrogen atoms.  Recall that carbon has 4 valence electrons available to bond.  An example is ethane. 



Note that all the atoms have full valence shells because they are sharing electrons. 

Single bonds are represented by dashes.

In alkanes, carbon atoms only form single bonds.  This means that two electrons are being shared between the two carbons.

The general formula of an alkane is CnH(2n + 2).  Cn represents the number of Carbon atoms in the chain.  H(2n +2) represents the number of H atoms in the molecule.  For example, in butane, there are 4 carbon atoms.  How many Hydrogen atoms are attatched to this structure? Use the equation '2n + 2'.  Therefore, there will be 10 Hydrogen atoms.  The molecular formula is C4H10. 



Butane: like the previous example, all the shells are full.

Another way to write this molecule(structural formula) is CH₃CH₂CH₂CH_3.
Because all the hydrogens have equal charges, the bond angles are always 109.5°(tetrahedral).

Naming Alkanes

The naming rules of organic compounds has been determined by IUPAC. 

To name them you first have to identify the longest chain of continuous carbons. It does not need to be straight, as long as it is the longest and isn't interupted.  

Next count the number of Carbon atoms in the chain.  Use the chart to determine the prefix.  Say there are 6 Carbons, the prefix will be 'hex'.  9 Carbons; the prefix is 'non'.

To specify that the compound is an alkane, and the suffix 'ane'.  It's easy to remember because the ending of 'alkane' is also 'ane'.

Note: This is called a homologous series.

For example:

1)Count: 5 Carbons. 

2)Look on list: prefix 'pent'. 

3)Add 'ane'. 

4)Name: pentane.

 

Let's do another.



Each vertice represents a Carbon atom.  Like before, the lines all represent single bonds.

1) Count: 9 Carbons.
2) Refer to list: prefix 'non'.
3) Add 'ane'.
4) Name: nonane.
5) Check.  Is there anything else attatched to the structure? No.

To see some chemical reactions involving alkanes, swatch the following video.
Combustion of Alkanes