A guide to naming organic compounds : Basics and saturated hydrocarbons

From A guide to naming organic compounds. This is Section 1:
Introduction and Saturated Hydrocarbons

Naming organic compounds is one of the more difficult tasks in grade 12 chemistry for me, so in the spirit of node your homework I'll see if I can explain it in order to gain a better understanding.

Because of the number of organic compounds, in 1892 the International Union of Pure and Applied Chemistry drafted a set of rules for the systematic naming of organic compounds. I will discuss the IUPAC system of nomenclature here.

I dare say the fundamental concept of this naming business is carbon chains. As you probably know, carbon likes to form long chains often known as hydrocarbons. Essentially in order to name a compound you need to find the longest carbon chain in the molecule.

Example 1:
              H H H H
              | | | |
            H-C-C-C-C-H
              | | | |
              H H H H
Example 2:
              H   H   H   H   H
              |   |   |   |   |
          H - C - C - C - C - C - H
              |   |   |   |   |
              H   H   H   H H-C-H
                              |
                            H-C-H
                              |
                              H
Example 3:
        H
        |
      H-C-H H   H   H
        |   |   |   |
      H-C - C - C - C - H 
        |   |   |   |
        H   H   H H-C-H
                    |
                    H

Example 1 above has a carbon chain of length 4, Example 2's chain is 7 carbons long and example 3's is 6 long. Even though a chain may bend around and stuff on the paper you count it as if it were straight.

After you have determined the length of the longest carbon chain you can then do the first part of naming the compound. Carbon chains each have names depending on their length. Here is a list of those names:

Prefix:			Number of carbon atoms in the chain:
Meth-			1
Eth-			2
Prop-			3
But-			4
Pent-			5
Hex-			6
Hept- or Sept-		7
Oct-			8
Non-			9
Dec-			10

Notice how I have only put prefixes? I'll get to the different suffixes and stuff in different sections, for now we'll just use -ane as our suffix.

So, in example 1 we had a carbon chain of length 4. That compound would be known as Butane and Example 2 is Septane because it has 7 carbons.

All that we have been looking at in this section are Saturated Hydrocarbons. Saturated Hydrocarbons are carbon chains that do not have functional groups nor double or triple bonds. Unsaturated hydrocarbons and functional groups are discussed in other sections.

Back to the contents:On to the next section