I found over the years that just giving the rules is overwhelming for naming organic compounds. If you just want the rules click here===> RULES.
I am going to take you through all the isomers of methane through octane.
Alkanes- Are saturated (all single bonds) hydrocarbons (hydrogen and carbon only).
The rule for naming is they all end with "-ane".
The general formula is CnH2n+2, n is the number of carbons is used to determine the number of hydrogen atoms. Example n=5, so H=(2(5) +2)=12
Homologous Series- Did you notice that as you go down from CH4 to C2H6 (and so on) the next member is different by 1 carbon and 2 hydrogen?
Now molecular formulas have limitations. You never really know how the molecule is constructed. So let's look at the structural formulas and name each.
The first 3 alkanes have no isomers (they can only be drawn 1 way). Makes for a good multiple choice question.
Naming Compounds- Ignore all the hydrogen's. We only worry about carbon atoms.
Isomers of Butane C4H10
Rule #1-Name the longest continuous chain of carbon atoms, and end it with -ane.
This is butane, but we call it
n stands for normal
Rule #2- Remaining side chains will be given the ending -yl. They are placed before the longest chain when naming.
The longest chain is 3 carbons, so "propane". There is one carbon left. We call this "methyl".
Isomers of Pentane C5H12
Rule #3- Multiple side chains will use prefixes 2 is di-, 3 is tri-, 4 is tetra- and so on.
Longest chain is 3, so propane
2 separate, one carbon side chains is dimethyl
Isomers of Hexane C6H14
WAIT....these are different structures with the same names...
Rule #4 When necessary use the lowest number to give the location of each side chain. You may have to number the longest chain from the right side to find the lowest number. (NOTE numbers and letters are separated by a hyphen)
Did you notice we had to number from the right? If we named from the left it would be 3,3-dimethyl butane.
2+2 vs. 3+3 always use the lowest numbers.
Isomers of Heptane C7H16
Again, each side chain gets a number. Since we have 3, one carbon side chains, it is called "trimethyl". You better have 3#'s when you have the tri prefix.
This has 1(2-carbon) side chain. It is NOT dimethyl. Dimethyl is 2(1-carbon) side chains. This is an "ethyl" group.
Notice I did not use a number. If was moved one carbon to the left...
The longest chain becomes hexane.
Isomers of Octane C8H18
(no number needed)
(number it from the right side)
Rule #5- When there are 2 different side chains name them in alphabetical order using the carbon prefix (meth, eth..).
(ethyl does not need a #, it can only go on carbon 3)