Alkanes and Nomenclature
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?
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
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
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”.
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.
IUPAC says it this way:
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).
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.
This covers most of the functional groups you’ll meet in Org1/Org2.
Notes
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.
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)
Lowest locant. 3-hydroxynonan-4-one
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.
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.’🙂
Why Ether is given less priority than HALO group?
I’ve seen other sites showing ether group above halogens.
Please clarify my doubt.
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.
This was very helpful.
The compound with the highest priority would also take preeminence when counting right?
Let’s say a compound like CH3CH2CHOHCH3
The example you give would be 2-butanol, since counting is done so as to give the lowest numbers to substituents.
Very helpful….tq
We wrote water symbol H2O, but we did not wrote OH2
Please reply this dout question.
Why is it CH4 and not H4C ? This too, I have no idea.
Plz make a animation on it
If one compound has chlorine and alkene . Which one can give first priority
Chloro, since it has higher alphanumeric priority.
Among alkoxy and alkyl which has higher priority in nomenclature?
The suffix will be the parent alkyl chain, -ane. Such as in ethoxyethane, or 2-methoxypropane.
Thanks, it’s very helpful.
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.
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?
Should we consider the alkoxy to be the ether group?
thanks!
When would we need to use carboxamide in naming an amide?
If it’s the only carbon on a chain. For instance if the amide is connected to cyclohexane. https://pubchem.ncbi.nlm.nih.gov/compound/cyclohexanecarboxamide
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.
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?
Did you read the part at the bottom? It’s directly from IUPAC.
Thanks
So you suggest we break into the IUPAC with Polyjuice potion?
Need to keep them on their toes every once in awhile.
Why phenol is not included?
The functional group present on phenol is an alcohol (OH). Phenol is not a distinct functional group.
Thanks 🙏🙇 for my concepts clear
OK, thanks Asra for letting me know.
Absolutely PERFECT table for the names of functional groups, this was just what I needed. Thanks so much!
Awesome, glad you found it useful David.
What about so3H, group
Below COOH, above anhydrides.
Sulphonic acid should come after carboxylate acid
Indeed it does.
I think alkyne should come before alkenes
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
Because the longest chain is 3 carbons long.
Which has highest priority
SO3H or -COOH….?
COOH. Section P-42 of the Blue Book. https://imgur.com/a/c9TjTQm
Well everything is fine, but i think sulphonic acid is missing which should be placed just below carboxylic acid. Thanks
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
Wrong in what way exactly?
Tq so much
This is wonderful! This website is so useful!
Anhydride is missing please tell about that… And also thanls a lot
Anhydride is below sulfonic acid but above ester. Section P-41
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.
All alkenes and alkynes are considered as a set for determining the lowest locant. When both alkene and alkyne are present, the -yne suffix will be used.
Which one we prioritise if we have three chlorine or bromine at one end of the chain and the carboxylic on the other end ?
Carboxylic acid. Highest priority.
Where do isonitriles fit in?
They are always prefixes (“isocyanato”) just like halides.
What does the (R) on the Ester prefix stand for?
The R-group (the organic substituent, e.g. ethyl or methyl or propyl…)
Where do phenol groups fall on this priority ranking?
Phenol is not considered a separate group. They are named as alcohols. OH is the functional group, and C6H5 is the parent hydride.
guys your table up till alcohols is right but after that it is wrong as after that the order is
thiol
amine
ether
sulphide
alkene
alkyne
alkyl hallide
nitro
alkane
Wrong.
James, again, thanks SO much for making OChem.understable.
Happy New Year :).
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
Below carboxylic acid. Above anhydride and above ester.
Why halogens are not included in this priority order?
Halogens are always prefixes.
Can you please provide an example where ester is not the primary functional group and name it?
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?
Where do epoxides fit into this list? Are they considered a substituant or a functional group?
I think it is good to provide this type of chart to the student because this help them in their study
So Thanks!!!
???????????????????????
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-
I think ether should be right after amines and alkane after nitro? some other website seem to say that, which one is correct?
Please give me a answer
Not correct. See section P-42 of the Blue Book.
where is – X in order
X stands for a halide group.
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?
It is false.
Where so3h must be placed
Just below carboxylic acids. See http://www.acdlabs.com/iupac/nomenclature/93/r93_326.htm
yes, you are right
Out of Sulphonic acid and carboxylic acid which would be given more priority?? Please tell the answer…i m little confused
Carboxylic acids. http://www.acdlabs.com/iupac/nomenclature/93/r93_326.htm
Carboxylic acid would be given more priority
Is the above given priority table authentic??
See http://www.acdlabs.com/iupac/nomenclature/93/r93_326.htm and http://www.acdlabs.com/iupac/nomenclature/93/r93_317.htm
This table agrees with information on those pages, from IUPAC’s “Blue Book”.
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.