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 it is: Table of Functional Group Priorities For Nomenclature
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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{ 40 comments… read them below or add one }
Animation makes it all the more interesting !
thanks.
I think ether should be right after amines and alkane after nitro? some other website seem to say that, which one is correct?
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
According to my view friend your thought is wrong because you should know that we write fg as prefix only when it has less priority and you can not use alkane as prefix. nitro group always remains in the form of prefix and ether vice versa. So fg having high priority is used in the form of suffix. Ether is not used as suffix so it has less priority than alkane. It will be after alkane and not after amine.
i think alkyne should come before alkene: it should be alkyne-alkene-alkane, decreasing unsaturation and increasing saturation…
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
If Halogens have higher perioity than Nitro why the Nitro group is written after the Bromine
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.
So does that apply to all the functional groups, in all cases?
It (alphabetization) only applies to substituents.
can anyone plz say what is d criteria for this table.????..
IUPAC.
well…but can u plz suggest me what r the criterias which IUPAC have applied???
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.
please give some example where carboxylic acid act as prefix .Will sulphonic acid be given more priority than carboxylic acid?
Can you please give example where carboxylic acid prefix ‘carboxy’ is used in nomenclature?
Can u please name this compound HOOC-CH²-CH²-CH²-CH(CH²-CH²-COOH)-CH²-CH²-CH²-COOH and HOOC-CH²-CH²-SO³H
Carboxy may be used when one of the chains attached to the root carboxylic acid also has the carboxylic acid functional group. E.g. 4-(Carboxymethylene)-2,5-heptadienedioic acid.
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
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.
Tie goes to the ene, but this might not have been a tie.
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’ ?
where would the halogens be in this table?
under the alkyl halide section, 2nd to last priority just above nitro.
Halogens come down at the rock botoom. They are not used as suffixes. Only Prefixes
Other websites show ethers as having higher priority than alkenes
http://www.chem.ucalgary.ca/courses/351/orgnom/functional/func.html
http://academics.keene.edu/rblatchly/OrgoCommon/hand/functgrps/Nomenclature.html
I agree, I think that ethers should be higher priority than alkanes. In the case of CH3OCH2CH3Ito should be named as ethyl methyl ether.
Thanks a lot! That really helped! :)
i have a doubt.suppose there’s a compound containing both alkene and alkyne functional groups. what gets higher preference?
Alkene, according to IUPAC.
If the carbon chain contains both the double and triple bond and they are both on the terminal carbons, then prioritization is given to the double bond. But if both double and triple bond are not on the terminal carbons, prioritization is given to the triple bond. These are called enynes.
Hey, in the 2nd example why do they use both the siffix and the prefix of nitromethane?
The alkane (” -ane “) has a higher priority than the nitro group, so the nitro group will not be used to a suffix.
Respected sir,
I have a doubt which may be small for you , but it brings more confusion if sulphonic acid and carboxylic acid are given which should be given priority first sir . sir please answer me and please give me a explanation.
Thanking you sir!
Carboxylic acid, according to this: http://www.acdlabs.com/iupac/nomenclature/79/r79_905.htm and this http://www.acdlabs.com/iupac/nomenclature/79/r79_469.htm
thanks a lot for reply but can you please explain In words
Can someone PLEASE suggest a mnemonic to learn this table?
I should give prioirity to br or alcohol
Alcohol, like it says in the table.