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Alkanes and Nomenclature

By James Ashenhurst

Table of Functional Group Priorities for Nomenclature

Last updated: March 21st, 2019

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 [source], 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
2-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.

3-applying the priority

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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Comment section

81 thoughts on “Table of Functional Group Priorities for Nomenclature

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

    1. 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.

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

    1. You’re right Christopher. I found this from a book I am using to study for my DAT exam. I hope it helps
      “Note: The group B functional groups (alkene and alkyne” are considered to have equal priority: in a molecule with both double and a triple bond, whichever is closer to the end of the chain determines the direction of numbering. In the case where each would have the same position number, the double bond takes the lower number. In the name, “ene” comes before “yne” because of alphabetization. See examples on the next page”

    1. 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.

        1. 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.

      1. 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.

  3. 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

    1. 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.

      1. According to: Principles of
        Chemical Nomenclature
        A GUIDE TO
        IUPAC RECOMMENDATIONS, Edited by G.J. Leigh

        Page 80-81:

        If double and triple bonds are present in a structure, they are considered together
        when assigning lowest locants. Only when this does not allow a resolution do double bonds receive the lowest locants.

        In a name, the ending -ene is cited before -yne, but
        with elision of the final ‘e’.

        12. HCC-CH=CH-CH3 pent-3-en-l-yne
        13. HCECCH=CH2 but-l-en-3-yne

  4. 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’ ?

    1. I agree, I think that ethers should be higher priority than alkanes. In the case of CH3OCH2CH3Ito should be named as ethyl methyl ether.

  5. i have a doubt.suppose there’s a compound containing both alkene and alkyne functional groups. what gets higher preference?

    1. 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.

  6. 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!

  7. Why NO2 is not taken as principal functional group , since the compound which is more withdrawing is considered to be as more powerful functional group!! So why is it so????

  8. Very informative and well organised….
    However it would be awesome if sulphonic acid and anhydrides could be added too :D
    They’re pretty superior
    Thanx though, this saved me a ton of time

  9. The so-called “Table of Functional Group Priorities For Nomenclature” can be misleading. It is not in accordance with past (1979, 1993) or present (2013) IUPAC recommendations.

  10. Out of Sulphonic acid and carboxylic acid which would be given more priority?? Please tell the answer…i m little confused

  11. This is for a true or false question:

    “Butanal” is another name for isobutanol.
    I am almost 100% certain this is false, but I just want to be sure that there is no way, or possible arrangement of the alcohol group (-OH) that can occur that would result in it being possible to name it like a aldehyde right?

  12. I think that the priority order of functional group is this :
    1. -COOH
    2. -SO3H
    3. -COOR
    4. -COX
    5. -CONH2
    6. -CN
    7. -CHO
    8. =C=O
    9. -OH
    10. -NH2
    11. =C=C=
    12. -C-=C-

  13. I think it is good to provide this type of chart to the student because this help them in their study
    So Thanks!!!

  14. Where do epoxides fit into this list? Are they considered a substituant or a functional group?

  15. In the ease of open chain compounds the secondary prefix is added just before the root word in the alphabetical order. why is it so?

  16. Your priority table is very very wrong. I think you should go study some more before misleading others. Please correct them our just remove the page

  17. Well everything is fine, but i think sulphonic acid is missing which should be placed just below carboxylic acid. Thanks

  18. When alcohol is on high priority than numbering should begin from alcohol. eg.
    BUT why can’t be 1-methyl Ethanol

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