Talk:Anomer

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Can something like beta-D-ribopyranose have an alpha anomer?

Ribopyranose doesn't have a CH₂OH group above the plane of its cyclic conformation, so no. Actually it can't even have a beta conformation. 84.197.144.27 15:47, 31 January 2007 (UTC)

This is incorrect, ribopyranose does have alpha and beta anomers. this is explained in the nomenclature section. defining the anomer does not require any specific group in any specific location, it only requires the presence of another asymmetric carbon in the ring. also see IUPAC gold book reference. Whmice (talk) 16:00, 7 August 2010 (UTC)

There is a problem with the explanation(s) of the definition of how one works out if a carbohydrate is the alpha or beta anomer. Two methods are discussed in the article; comparing the absolute configurations of the anomeric centre and the anomeric reference atom, and comparing if the hydroxyl groups on the anomeric centre and the anomeric reference atom are cis or trans relative to each other. Both of these methods are true when the anomeric centre and the anomeric reference atom are C1 and C5 respectively, but when this is not the case (eg arabinose), they contradict each other. Looking at the reference data from IUPAC, it appears to me that comparison of the absolute configurations is the only definitive method of working out the anomeric configuration. Could others let me know if they agree with this explanation before I try to tidy up the article? --The chemistds (talk) 21:04, 5 May 2011 (UTC)

Honestly, i don't suppose even half the population here knows what you are talking about.

Just tidy up the article! Please! *begs on bended knees* Neeya The Great (talk) 15:02, 27 May 2011 (UTC)Neeya the Great

Way too technical! Simplify things? Please?

Dear author: I have to agree with the students here. I suggest you start with the Fischer projection material omitting the technical definition at the top which may be simplified and included later:" In the Fischer projection OF A CYCLIC SUGAR (see [1]) the exocyclic oxygen atom IS at the anomeric centre. ITS CARBON IS THE ANOMERIC REFERENCE ATOM. AS SHOWN IT IS IN THE cis (on the same side) POSITION to oxygen OF THE OH GROUP. THIS CONFIGURAGTION IS the α ANOMER. If the two oxygens are trans (on different sides), the CONFIGURATION is THE β ANOMER Tdw1203 (talk) 19:25, 8 August 2014 (UTC) Tdw1203 (talk) 19:27, 8 August 2014 (UTC)

I don't know what an anomer. It came up in an MCQ as an option in my textbook... in organic chemistry regarding Isomerism... Yet here, the article primarily deals with everything else but Isomerism. So will someone knowledgeable in this field kindly simplify things for ... let's see... schoolchildren(...?) here? Please?

Sincerely, stuck-hopelessly-trying-to-understand Neeya The Great (talk) 14:58, 27 May 2011 (UTC)Neeya The Great

I second the opinion above. With my limited organic chemistry, I am trying to figure out the difference between a reducing and non-reducing disaccharide, which requires knowing something about anomers. Unfortunately, this article is too technical and relies excessively on links to other articles. It can be very confusing and time-consuming to use these links (and their links) to eventually understand the original article. 2Plus2Is4 (talk) 17:52, 2 April 2013 (UTC)

Mechanism arrows wrong direction

The arrows in the first step of the second mechanism using an amphoteric molecule are all pointing in the wrong direction.

absolute configurations of the anomeric carbon and the reference atom

"If the absolute configurations of the anomeric carbon and the reference atom are compared, then both are the same (R,R or S,S) in the α anomer and different (R,S or S,R) in the β anomer." I am pretty sure that it's just the other way around, the α-D-glucopyranose has a R-configuration at the anomeric carbon and a S-configuration at the reference atom. Therefore, both are the same (R,R or S,S) in the β anomer and different (R,S or S,R) in the α anomer. Please correct me if I'm wrong... — Preceding unsigned comment added by 129.70.152.189 (talk) 14:27, 22 August 2014 (UTC)

If there is a consistent relationship between R/S and alpha/beta then you are correct (that's consistent with the examples I've checked). The source for the statement you are quoting is wrong and has a picture illustrating alpha glucopyranose where it misidentifies two centers which are R and S as being the same. I'm not sure that there is a consistent relationship though. Very few sources and none of what I would consider the most reliable ones (like goldbook) mention R/S. Instead they describe it in terms of what the Fischer projections look like. If a third person comes along and agrees I would say that part should be edited out to avoid wrong information at least, but a source would be needed to make the R/S = alpha statement and I haven't seen one anywhere. 134.147.63.110 (talk) 20:56, 28 July 2018 (UTC)

I have gone ahead and removed the relevant wrong section after rechecking myself. I could not find a source for the inverse (i.e. alpha = different configuration) but by extrapolating from the formal definition as described in the article (cited below), it is true for all sugars that do not have substituents heavier than O (starting with C=O) on their tail (high-locant) end.

"If in the cyclic Fischer projection the exocyclic oxygen atom at the anomeric centre is cis (on the same side) to the exocyclic oxygen attached to the anomeric reference atom (in the OH group) the anomer is α. If the two oxygens are trans (on different sides) the anomer is β." Haeuslebauer (talk) 15:25, 16 November 2024 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Anomer/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Anomers are identified as "α" or "β" based on the relation between the stereochemistry of the anomeric carbon and the furthest chiral centre in the ring. The α anomer is the one in which these two positions have the same configuration; they are opposite in the β anomer.[2] Thus the structure of α-D-glucopyranose has opposite stereochemistry at both C1 and C5 whereas β-D-glucopyranose has the same stereochemistry at C1 compared to C5. This relationship is strictly based on the absolute stereochemistry, not cis/trans relationships or axial/equatorial positioning in the ring conformation. In α-L-arabinopyranose, the absolute configurations are still the same even though the position of the anomeric oxygen is different than in α-D-glucopyranose.

Last edited at 18:16, 17 August 2009 (UTC). Substituted at 07:57, 29 April 2016 (UTC)

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