Table of Functional Group Priorities for Nomenclature

by James

in Alcohols, Aldehydes, Alkanes, Alkenes, Alkyl Halides, Alkynes, Carboxylic acids, Esters, Functional Groups, Ketones, Nomenclature

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?

1-dilemma

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 it is: Table of Functional Group Priorities For Nomenclature
nomenclature priority

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.

This covers most of the functional groups you’ll meet in Org1/Org2, if you run into a thioketone or some other bizarre entity, you’ll probably want to see Reusch or Wikipedia.

 

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{ 19 comments… read them below or add one }

abhi November 8, 2011 at 7:25 am

Animation makes it all the more interesting !

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deepak December 21, 2011 at 1:34 pm

thanks.

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IP June 18, 2013 at 6:34 pm

I think ether should be right after amines and alkane after nitro? some other website seem to say that, which one is correct?

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james June 19, 2013 at 9:11 pm

With amines, the suffix “ine” is used, but when nitro groups or ethers are present, the alkane suffix is used: http://www.acdlabs.com/iupac/nomenclature/93/r93_322.htm

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christopher unyime ebong September 25, 2013 at 10:41 am

i think alkyne should come before alkene: it should be alkyne-alkene-alkane, decreasing unsaturation and increasing saturation…

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James Ashenhurst September 25, 2013 at 10:24 pm

Alkene does go first over alkyne, but I believe it is due to the alphanumeric priority of -ene over -yne and not based on the extent of saturation: http://www.chem.ucalgary.ca/courses/350/Carey5th/useful/nomen.html

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Ptachia Bar-On October 6, 2013 at 5:28 pm

If Halogens have higher perioity than Nitro why the Nitro group is written after the Bromine

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James Ashenhurst October 9, 2013 at 9:33 am

It’s just due to alphabetization. For example we would number 2-bromo 3-nitro butane based on the fact that bromine is higher up in (our) alphabet than nitro.

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Birupakshya Singh December 26, 2013 at 2:52 am

can anyone plz say what is d criteria for this table.????..

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James Ashenhurst December 27, 2013 at 12:58 am

IUPAC.

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Birupakshya Singh January 21, 2014 at 3:02 am

well…but can u plz suggest me what r the criterias which IUPAC have applied???

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James January 21, 2014 at 12:29 pm

I believe it is at least partially based on oxidation state, with higher oxidation state having higher priority. But that doesn’t explain why alkenes are higher priority than alkynes. Nomenclature is a human convention.

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Rani January 11, 2014 at 1:06 pm

please give some example where carboxylic acid act as prefix .Will sulphonic acid be given more priority than carboxylic acid?

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Govind Pradeep January 15, 2014 at 11:33 am

Why does alkyne have more priority ovr alkene? Because i have seen compounds where the least no: is given to alkynes ie., they hav been given most priority ovr alkene..for example, 6-chloro-4-ethyl-5-methylhept-5-en-1-yne

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Rich July 6, 2014 at 3:18 pm

The yne might have been given priority in this case because the parent chain could be numbered in such a way to make one of the unsaturations C1, and it happened to be the yne and not the ene.

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Rich July 6, 2014 at 3:18 pm

Tie goes to the ene, but this might not have been a tie.

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Rich July 6, 2014 at 3:16 pm

Since ethers are “substituent-only” (named only by prefix), are peroxides prefix-only as well? What about epoxides? (I think that’s a little less clear, eg. oxirane.)

How would a peroxyacid RC(=O)OOH (“peracid”) or a perester RC(=O)OOR’ be handled?

I’m guessing a carbonate ROC(=O)OR’ takes priority over an ester RC(=O)OR’ ?

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s.brar October 21, 2014 at 8:52 pm

where would the halogens be in this table?

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Blank November 3, 2014 at 12:03 pm

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