Here’s a little nomenclature dilemma.
Let’s say you’re trying to name a molecule. You’re familiar with the familiar naming suffixes like -ol, -ene, -ane, -oic acid and so on. But then you come across a molecule which has multiple functional groups.
What do you do? What suffix do you give the molecule?
We need some kind of priority system for nomenclature. And so, IUPAC has developed one. If you have a molecule with, say, a carboxylic acid and a ketone you consult the table. The functional group with the highest priority will be the one which gives its suffix to the name of the molecule. So in example #1 above, the suffix of the molecule will be “-oic acid” , not “-one”, because carboxylic acids are given higher priority. However, if a ketone is present with an alcohol (example 3) then we will use the suffix, “-one” because ketones have a higher priority for nomenclature than alcohols.
[You might ask: what is this based on? It's an arbitrary agreement by IUPAC, although note that there is some correlation between the oxidation state of the carbon and the priority (more oxidized groups tend to be higher priority). However this really is an example of something you have to either look up , memorize, or have a computer do for you. It's not conceptual. ]
Here are some examples of applying the order of functional group priorities to solve nomenclature problems. The highest ranked functional group becomes the suffix – it’s highlighted in red.