Search
Searching...

Alkanes and Nomenclature

By James Ashenhurst

Table of Functional Group Priorities for Nomenclature

Last updated: December 13th, 2022 |

How To Determine Which Functional Group Has “Priority” For Naming Purposes

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?

iupac-nomenclature-which-group-takes-priority

We need some kind of priority system for nomenclature. And so, IUPAC (think of the “Ministry  of Magic”, but for chemists) has developed one. If you have a molecule with, say, a carboxylic acid and a ketone you consult the table. T

he 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. ]  See Note 1. 

Highest Priority Groups:  Carboxylic Acids, Sulfonic Acids, Esters, Acid Halides, Amides

table-of-functional-group-seniority-priority-for-iupac-nomenclature

Note that with the exception of sulfonic acids, these are all carboxylic acid derivatives. IUPAC goes  into way more detail than we need to here.

The “seniority rules” continue in the following order, where we are cherry-picking the most common examples. [Note 2]

Next In Line: Nitrile, Aldehyde, Ketone, Alcohol, Thiol, Amine

functional-group-priorities-seniority-for-nomenclature-nitrile-aldehyde-ketone-alcohol-thiol-amine

Again, this is not a complete list – we’re cherry picking the most commonly encountered functional groups here.

Alkenes And Alkynes

If carbon-carbon multiple bonds are present in the molecule, they are considered as substituents with a priority (or “seniority”, according to IUPAC) lower than that of amines.

So for a molecule with an alkene and an  alcohol, the alcohol has priority and the molecule has the suffix, “-ol”. The presence of the double bond is noted with the locant followed by the prefix, “en-“. For example, pent-4-en-1-ol.

If no higher-priority groups are present, the suffix for a molecule containing an alkene will be “-ene”, such as in pent-1-ene.

For an alkyne, the corresponding prefix is “-yn” and the suffix is “yne”.

alkene-alkyne-nomenclature-en-prefix-ene-suffix-yn-prefix-yne-suffix

At this point the methodology for naming molecules changes slightly. In the absence of one of the above functional groups, the suffix will always be “-ane”, “-ene”, or “-yne”, depending on whether any unsaturation is present in the molecule, and any lower-ranked substituents will be prefixes.

Alkenes vs. Alkynes: Which  Takes “Priority”?

This brings us to a common source of confusion in nomenclature. When an alkene and an alkyne are present in a molecule, which takes priority?

It  depends on what you mean by “priority”.

For the purposes of the name, “-ene” comes before “-yne” alphabetically. So when an alkene and an alkyne are present in  the same molecule, the ending will always be “yne”. 

For the purposes of numbering, if there is a tie between an alkene and an alkyne for determining the lowest locant, the alkene takes priority.

alkene-and-alkyne-naming-which-group-takes-priority

IUPAC says it this way:

iupac-says-that-ene-takes-priority-over-yne-in-the-event-of-a-tie-for-numbering-purposes

Right. Let’s move along to the other functional groups.

Functional Groups That Are Always Prefixes: Halides, Alkoxides, Azides, Nitro

Some functional groups have been deemed unworthy of ever getting their own suffixes. For nomenclature purposes, they are forever out of the limelight, subservient to the -ane, -ene, or -yne ending of the parent hydrocarbon  (or “parent hydride”, as IUPAC calls it).

These groups include the halides (bromo, chloro, fluoro, iodo), ethers (“alkoxy”), azide and nitro functional groups. Source: Table 5.1, Section P-59.1.9 of the 2013 Blue Book (Page 630).

functional-groups-that-are-always-prefixes-halides-ethers-azides-nitro

Some Examples With Multiple Functional Groups

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.

examples of applying iupac nomenclature functional group priority

This covers most of the functional groups you’ll meet in Org1/Org2.

Notes

Related Articles

Note 1. This article takes into account the latest recommendations of the IUPAC Blue Book  (2013 edition)] 

Note 2. . Just for the record these “rules for  seniority” can  be found in section P-41 of the Blue Book, page 428 of the 2013 edition. 

 

00 General Chemistry Review
01 Bonding, Structure, and Resonance
02 Acid Base Reactions
03 Alkanes and Nomenclature
04 Conformations and Cycloalkanes
05 A Primer On Organic Reactions
06 Free Radical Reactions
07 Stereochemistry and Chirality
08 Substitution Reactions
09 Elimination Reactions
10 Rearrangements
11 SN1/SN2/E1/E2 Decision
12 Alkene Reactions
13 Alkyne Reactions
14 Alcohols, Epoxides and Ethers
15 Organometallics
16 Spectroscopy
17 Dienes and MO Theory
18 Aromaticity
19 Reactions of Aromatic Molecules
20 Aldehydes and Ketones
21 Carboxylic Acid Derivatives
22 Enols and Enolates
23 Amines
24 Carbohydrates
25 Fun and Miscellaneous

Comments

Comment section

153 thoughts on “Table of Functional Group Priorities for Nomenclature”

  1. I have a question.
    Will lowest locant rule will be prefered or the order of preference of functional group will be preferred. I mean H3CCH2(OH)CHCOCH2CH2CH2CH2CH3.
    will be named 3-hydroxynonan-4-one(locant rule followed)
    Or 7-hydroxynonan-6-one (order of preference followed)

    Reply
  2. Pingback: Best 17 Alkene Group List - Edu Learn Tip

  3. But if you look at the examples below ”Carefully” you will notice, numbering is as simple as we’re trying to make it.😂

    Example: 1-Bromo-3-Methoxypropane.
    Example*: 1-butoxy-5-chloropentane.

    Example: 1-Ethoxy-3-iodopropane.
    Example*: 1-Chloro-3-propoxypropane.

    Example: 1-Chloro-3-nitropropane
    Example*: 1-iodo-3-nitropropane

    *Examples does not contradict the ALPHABETICAL rule.

    Reply

  4. But if you look at the examples below ”Carefully” you will notice, numbering isn’t as simple as we’re trying to make it.😂

    Example: 1-Bromo-3-Methoxypropane.
    Example*: 1-Chloro-5-butoxypentane.

    Example: 1-Ethoxy-3-iodopropane.
    Example*: 1-Chloro-3-butoxypropane.

    Example: 1-Chloro-3-nitropropane
    Example*: 3-iodo-1-nitropropane

    *Examples just contradict the ALPHABETICAL rule.

    I think it depends on the OXIDATION State of the Carbon.
    ‘If a substituent Oxidises the Carbon more than other substituent on the same position, then numbering will start from that substituent which Oxidises more.’🙂

    Reply

  5. Why Ether is given less priority than HALO group?
    I’ve seen other sites showing ether group above halogens.
    Please clarify my doubt.

    Reply

    1. In the case of halogens and ethers it’s the alkane which has highest priority (the suffix) and the halogens / alkoxy groups are prefixes that will be ranked based on alphabetical order. Depending on whether or not the halogen substituent is above or below the alkoxy alphabetically is the key thing.

      Reply
  6. Pingback: Is COOH a functional group?
  7. Pingback: What is a COOH group called?

  8. This was very helpful.

    The compound with the highest priority would also take preeminence when counting right?

    Let’s say a compound like CH3CH2CHOHCH3

    Reply

  15. When do you use oxo or formyl when naming aldehydes. It seems different sources say different things.What I have seen that makes the most sense is to use formyl when the aldehyde is not part of main parent chain and use oxo when it is.

    Reply

  16. 3 questions
    1.)How do you find the parent chain for a molecule that has multiple double and triple bonds along with a functional group?I assume you find the longest chain that contains the functional group but also contains as many of those multiple bonds as possible?Is this correct?
    2.)Regarding carboxamide- As always, we look for the longest chain that contains the functional group, but in this case the longest chain that contains the functional group of amide is the single carbonyl carbon of the amide?That is why we call it carboxamide?

    3.)This question refers to compounds with multiple functional groups-When a functional group is lower priority and is named as a substituent, do we consider the carbon(if the functional group has a carbon) a part of the longest chain of the branched substituent?
    An example I don’t understnad: 3-(formylmethyl)hexanedial
    Why is the carbon on the substituent aldehyde not considered a part of the longest chain of the branched chain?
    The way I have leaned to treat branched non main chain substituents is to treat the first carbon coming off the main branch(as the number one carbon) and then count the longest continuous carbon chain to make the alkyl, alkenyl, or alkynl substituent the main name. Then what ever other branches exist off that main chain you give a locant,a name, and then arrange them alphabetically.So what gives?

    Reply

  20. Okay sir. If I get it right. On the table, alkene comes before alkyne but while naming molecule with both alkene and alkyne, alkyne will be the suffix. The one that is closer to the terminal carbon will take the least number and in case of a tie, alkene will have the least number. Is that so?
    Thanks in anticipation.

    Reply

  21. Sir, you claimed Alkene comes before alkyne in the priority table. But at the same time, you said if we have both alkene and alkyne in a molecule, yne will be the suffix. Is that not a contradiction?

    Reply
  23. Pingback: Chemical Compound Suffixes - Chemical Literature

  27. Absolutely PERFECT table for the names of functional groups, this was just what I needed. Thanks so much!

    Reply

  31. When alcohol is on high priority than numbering should begin from alcohol. eg.
    CH3CH(OH)CH3.
    IUPAC NAME – 2-PROPANOL
    BUT why can’t be 1-methyl Ethanol

    Reply

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

    Reply

  34. 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

    Reply

  38. alkynes have priority over alkenes. During nomenclature of long chain carbon compounds, numbering done in such a way as to locate double or triple bond by shortest route. Doesn’t matter which functional group arrive first. In any way alkynes are preferred over alkenes.

    Reply

  39. Which one we prioritise if we have three chlorine or bromine at one end of the chain and the carboxylic on the other end ?

    Reply

  45. In this priority table,Sulphonic Group(Functional Group) is not present.

    I want to know what is the real place of sulphonic group according to IUPAC

    Reply

  48. 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?

    Reply

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

    Reply

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

    Reply

  51. 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-

    Reply

  52. 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?

    Reply