Alcohols, carboxylic acids, esters, alkanes etc are classes of organic compounds, not functional groups, no? (alkanes contain no functionl groups!)

In other words, a class is a type of compound, while functional groups specifically refer to a group of atoms (or more generally a bonding sequence).

However, it appears that both are mixed up very frequently. So are alcohols both the class and the functional group? Or is this an example of bad language?


Alcohol is a functional group that you are probably familiar with.

From: https://kpu.pressbooks.pub/organicchemistry/chapter/2-3-functional-groups/

Instead, the table in the above link says "class" instead.

The sentences below sounds correct however (perhaps if a possessive is added: alcohol's, ether's, thiol's):

The alcohol functional group involves an oxygen atom that is bonded to one hydrogen atom

The ether functional group consists of an oxygen atom that forms single bonds with two carbon atoms.

The thiol functional group contains a sulfur atom bonded to a hydrogen atom.


I do see certain exceptions like ether referring to both the class, and the functional group (formally, alkoxy group). Perhaps this happens often for more complicated compounds; then it slowly encroached upon simpler ones....

Phenyl vs phenol functional group?

What is a functional group?

Inter-classification of organic chemistry functional groups (carboxyl vs alcohol & ether vs ester)

Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995) (http://dx.doi.org/10.1351/pac199567081307)

10.1 - What are the 'functional groups' and 'classes' of organic compounds? https://youtu.be/tL_KSmwIm2I

An article provides nice intuition on the 'functional group approach' https://www.chem.fsu.edu/chemlab/chm1046course/functional.html

  • $\begingroup$ I think the term class is sometimes also used to refer to the compounds containing a specific functional group because LibreTexts has used yet another word family that adds to the confusion. $\endgroup$ Jul 15, 2023 at 6:08
  • $\begingroup$ @Proscionexium I see that family is an even broader classification according to the elements present in the functional group $\endgroup$
    – Cheng
    Jul 15, 2023 at 8:15

2 Answers 2


In some cases, there is a clear correspondence between class and functional group. Alcohols are a class of compounds that all contain a hydroxyl functional group. The carbonyl functional group is an example where it gets more complicated. If a single carbonyl functional group is located at the end of a chain, we get an aldehyde, otherwise a ketone. Also, if the carbonyl functional group is combined with additional heteroatoms (i.e. something other than carbon or hydrogen), we use new names for these functional groups such as ester or amide or thioester.

There are also classes of compounds that contain multiple functional groups such as carbohydrates or dicarboxylic acids. In the end, the nomenclature has to support the amazing complexity and diversity of organic compounds that exist or are dreamed up.

However, it appears that both are mixed up very frequently.

Yes, sometimes it is easier to say alcohol-group instead of hydroxyl. In any field, there will be jargon and day-to-day usage that diverges a bit from the official terms. Also, as organic chemistry is developing, there might be functional groups or compound classes that are novel, and language describing them might change over time.


I think I have two points which can near what answer your question.

  1. The term functional group mainly refers to a group of atoms which imparts certain physical and chemical properties when attached to an organic molecule. So based on these alcohols, acids, esters etc. are called functional groups.

  2. Classes as said by @Proscionexium, is used to refer to a group of compounds having similar chemical properties (because of functional groups as stated before) but may have different physical properties (which could be due to different molecular mass etc). For example, consider a series C(n)H(2n+1)-COOH, all the compounds can be termed as a class of mono carboxylic acid as they show similar chemical properties.

I hope my answer could clear up your confusion .

  • $\begingroup$ +1, but I would strike that functional groups impart physical properties. Of course they do in the end, but the main point is chemical properties. Ethanol and decanol hardly share any physical properties. $\endgroup$
    – Karl
    Jul 16, 2023 at 9:25

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