How do you name alkanes, alkenes, and alkynes?

1 Answer
Mar 19, 2018

Consider the number of carbon atoms in the main carbon chains, and then any functional groups.


Start by finding the longest carbon chain in the molecule. Then you can use this to find the main name of the molecule. If the longest carbon chain is:
1 = methane
2 = ethane
3 = propane
4 = butane
5 = pentane
6 = hexane

And so on. If the molecule is an alkane, and has no other functional groups coming off it, then this is the name of the molecule. Then you consider if there are any more carbon atoms coming off the carbon chain. Depending on the number of carbons on this side chain you can call it by the following:
1 = methyl
2 = ethyl
3 = propyl
4 = butyl

You then need to find what place this group is on the original carbon chain. If there is more than one, you need to also find the number of this group. The numbers should be the smallest possible, when choosing which side of the carbon chain to call carbon 1. You can add this onto the front of the name. For example if you had a butane molecule and an ethyl group on the 3rd carbon along, you would name the molecule 2-ethylbutane. If there were 2 ethyl groups on the butane molecule on the 2nd and 3rd carbon it would be 2,3-diethylbutane.