Talk:Diastereomer

The following explanation given in the article is wrong: "In simple terms two stereoisomers are said to be diastereoisomers of each other if only one stereogenic centre differs between the two stereoisomers. It's a definition of an epimer.

References:

- Garrett, Grisham "Biochemistry" ("Pairs of isomers that have opposite configurations at one or more of the chiral centers but are not mirror images of each other are called diastereoisomers", 2nd ed., 1999, p. 213)

- McMurray "Organic Chemistry"

• The distinction is exactly one for an epimer and one or more stereocenters for the Diastereomer, I have added your reference and definition V8rik 20:28, 28 November 2006 (UTC)

congrads

--212.49.92.124 08:59, 19 July 2007 (UTC)ithink the article in diastereomer is a great one and actually easy to understand. grreat job --212.49.92.124 08:59, 19 July 2007 (UTC)

Problem with Fischer Projections

Either the Fisher Projections are not following convention (vertical, into page; horizontal, out of page), is plain wrong, or conflicts with the article on Fisher Projections. Can someone fix the pictures.

• I am unable to see anything wrong with the image, convert the first row Fisher images by a 90 degrees rotation around the carbon chain axis and you will see they are identical with the second row depictions. Lets have discussion first V8rik (talk) 17:26, 12 December 2007 (UTC)

You are absolutely right. It was my misunderstanding of Fisher projections which was the problem. The only reason I removed the image--I would of had a discussion first--was I didn't want any false information on Wikipedia. I'm sorry for the confusion. Keep up the good work. Jabin1979

• Thanks for your reply, I am glad the issue is resolved V8rik (talk) 17:26, 26 December 2007 (UTC)

reword

May I suggest a slight re-wording of the following sentence: "the number of configurational isomers of a molecule can be determined by calculating 2n, where n=the number of chiral centers in the molecule. This holds true except in cases where the molecule has meso forms." to "the number of configurational isomers of a molecule can not be more than 2^n, where n equals the number of chiral centers in the molecule. The number of stereoisomers realized is less than 2^n by the number of meso forms." Gaedheal (talk) 16:21, 5 November 2009 (UTC)

Erythro/threo

IMHO the definition of erythro and threo is wrong. "Two common prefixes used to distinguish diastereomers are threo and erythro (which correspond to the more intuitive anti and syn labels, respectively)." I believe it is the other way round - threo = syn and erythro = anti. —Preceding unsigned comment added by 86.31.187.255 (talk) 15:22, 12 December 2010 (UTC)

• I have checked the text against a textbook on this topic and statements made are correct (threo = anti) V8rik (talk) 17:48, 13 December 2010 (UTC)
• It would help knowing which textbook that is. At least and say that erythro = anti. I am therefore changing the article. All the rest of the text and examples already in the page agree with this. --AngelHerraez (talk) 14:36, 7 July 2011 (UTC)

And IUPAC says:

This notation is derived from carbohydrate nomenclature. The extension of this system has given rise to conflicting interpretations of these prefixes. It is recommended that for such cases the l, u or R *, S * system should be used.

• Now that I checked the page history I can see this has been controversial several times, so I'll try to document it. IUPAC defines 'anti' as: Two substituents attached to atoms joined by a single bond are anti if the torsion angle (dihedral angle) between the bonds to the substituents is greater than 90°. This clearly matches the top image for D-erythrose in this wiki article. Therefore, anti = erythro. So, the substituents are on different sides in the zig-zag formula, but on the same side in the Fischer formula. This matches what was said in the article; maybe the confusion came from Fischer vs. zig-zag? The cited book by Anslyn (which seems to be the support for rejection of the change) says on page 635: …while E-enolates give predominately anti (or erythro)…. Images of threonine also agree with this, since they are syn, while allo-threonine images are anti. --AngelHerraez (talk) 22:34, 7 July 2011 (UTC)
• The structures of threonine shown are non-superimposable mirror images of each other, hence enantiomers. The 2R,3R and 2S,3S structures should be shown instead. 173.75.37.125 (talk) 19:54, 3 December 2011 (UTC)mills

The image of D-threonine is confusingly not aligned with the L- enantiomer. I believe the point would be better made if the image showed the groups in the same locations & only the carbon-nitrogen bond changes (from solid wedge to dashed wedge). I would do it myself but don't have experience editing SVGs. ~DΦC (talk) 03:40, 7 January 2023 (UTC)

• To reiterate, the distinction of erythro/threo is confusing because the L/R images are flipped. It's best to present the information in a way that highlights the important aspect (the nitrogen bond's orientation relative to the larger molecule). I would even suggest separating the L/R from each other unless showing both is important to actually understand E/T. ~DΦC (talk) 03:49, 7 January 2023 (UTC)

Confihuration and mirror images

Diastereomerism occurs when two or more stereoisomers of a compound have different configurations at one or more (but not all) of the equivalent (related) stereocenters and are not mirror images of each other.

The above quote from the first paragraph is stating the same point in two different ways: when al chiral centers have the opposite configuration, the molecule will be transformed in its mirror image, as far as I know, so the last part of it not needed to make the point. On th eother hand, indicating its truth would not harm, when related to the twisting of the conformations.T.vanschaik (talk) 10:56, 9 February 2012 (UTC)

Comparation w/ enantiomers

"Diastereomers have different physical properties and different reactivity, unlike enantiomers."

enantiomers show different reactivity when space comes into account (biological, catalysis, etc), you can see this in the enantiomers page... i'm rephrasing this — Preceding unsigned comment added by 168.96.204.43 (talk) 19:41, 19 March 2012 (UTC)

Erythro and threo

These are NOT the IUPAC descriptors for relative stereochemistry. There are multiple reasons: There are multiple requirements for erythro and threo to be valid: 1. The principal carbon chain cannot be assigned an erythro/threo descriptor. 2. Only substituents of the highest priorities can be compared. 3. Substituents must be adjacent. Therefore we now use syn and anti. SEE http://goldbook.iupac.org/E02212.html "Descriptors of the diastereoisomers of an acyclic structure or partial structure having two stereogenic centres. This notation is derived from carbohydrate nomenclature. The extension of this system has given rise to conflicting interpretations of these prefixes. It is recommended that for such cases the l, u or R*, S* system should be used." ★Ffgamera★ - My page! · Talk to me!· Contribs 13:46, 4 July 2013 (UTC)

I updated the article to say exactly what that authoritative ref says regarding when (not to) use it. DMacks (talk) 09:47, 13 July 2013 (UTC)

What about cis-trans alkene isomers?

Its strange that this decription of the definition of a diastereomer does not mention E/Z alkene isomers!--175.38.163.188 (talk) 18:26, 15 August 2013 (UTC)

Cis–trans isomerism does not involve chirality. So the E and Z forms are isomers, but not enantiomers, and as such can't be diastereomers either. Project Osprey (talk) 21:38, 15 August 2013 (UTC)

Is that right?--175.38.163.188 (talk) 06:22, 16 August 2013 (UTC)

IUPAC definition of Diastereomer = Stereoisomerism other than enantiomerism.

IUPAC definition of Stereoisomerism = Isomerism due to differences in the spatial arrangement of atoms without any differences in connectivity or bond multiplicity between the isomers.

Result = E and Z isomers ARE diasteromers!--175.38.163.188 (talk) 07:54, 16 August 2013 (UTC)

• Actually, yes. Sorry! I probably shouldn't try and answer these sorts of problems on my way to bed. I'll try and sort it out on Sunday. Project Osprey (talk) 23:27, 16 August 2013 (UTC)

Yer, I am guilty of similar things too. I'll take that as consensus for addition then!175.38.163.188 (talk) 07:04, 17 August 2013 (UTC)

Etymology of Erythro and Threo?

Erythro seems almost certain to be derived from Greek eruthro- meaning "red" which turns up in various scientific terms, but even assuming this to be the case, finding a confirming (or denying) source has proven difficult.

Threo is even more difficult as it doesn't seem to be well-attested anywhere. It looks as though it might also be Greek, but if it is, there's slim to no usage of the prefix in literature. Furthermore, the apparent conjugations of what there is do not seem to match those of erythro. Sister site Wiktionary has an entry for the term, but is also lacking / requesting an etymology.

If not Greek, one possibility is that it's derived from an anagram of erythro; there is at least one other example of new scientific terms being created through anagrams of others. (Specifically, I'm thinking of the spider genera Tegenaria and Eratigena for which the latter is a deliberate anagram of the former).

While it's not strictly necessary to have the etymology of scientific terms, I believe it could be a worthwhile addition if only a source could be found. Cyrek (talk) 21:29, 13 November 2018 (UTC)

Wiki Education assignment: Honors Organic Chemistry I

This article was the subject of a Wiki Education Foundation-supported course assignment, between 22 August 2022 and 2 December 2022. Further details are available on the course page. Student editor(s): Jonestj, Namireddy, Hjwtony (article contribs).

— Assignment last updated by 123pickles456 (talk) 01:08, 10 October 2022 (UTC)