Talk:Chirality (chemistry)

The comment about the natural chirality of sugars may be incorrect. The entry on [Optical Rotation] states that there are natural sugars of both chirality.

Are the Pictures correct?

Using the "CORN" method for amino acids, is the picture in the left hand really an L-amino acid, and is the picture in the right hand, really a D-amino acid?? BillChia (talk) 13:23, 24 February 2010 (UTC)BillChia, 24 February 2010.

Why

No mention of what explanations are being hypthesised for the right-handedness of biology. Two I know of are

1. it just turned out that way
2. the weak nuclear force makes one way more low energy that the other

Pmurray bigpond.com 06:03, 12 September 2005 (UTC)

Yes

Biology is right handed? NPR's Science Friday said all multicellular life on Earth uses "left-handed" amino acids.--64.107.201.150 19:49, 29 June 2006 (UTC)

Different parts of "biology" (as a whole) have different handedness (assuming that means "sign of optical rotation" or "correspondence to certain stereocenters"?). The Chirality article doesn't describe biology as being any particular handedness, so when someone finally answers the question, just have to make sure to avoid introducing any such generality. DMacks 02:02, 6 July 2006 (UTC)

It should probably be amended that ALL amino acids are L type rather than just most. from Chiral Recognition in the Gas Phase, Powis p23. The only possible exception would be from Cysteine where the chirality is impeded by steric hindrence from the bulky sulphur group. 128.243.253.116 (talk) 22:31, 3 May 2011 (UTC)

Merge?

Would it make sense to merge material from Enantiomer? --Tabor 18:22, 18 October 2005 (UTC)

I think so, I will add the proposed merge template to both pages. --Aaronsharpe 11:12, 22 June 2007 (UTC)

• this merge proposal is not valid, you cannot have merge discussions lasting 1.5 years. tag removed V8rik 19:39, 22 June 2007 (UTC)

I have put the tags back and if no one comes up with a good reson not to I will complete the merge in the next few days. TomViza (talk) 19:56, 3 June 2008 (UTC)

If you merge enantiomer into this article, you should merge diastereomer and atropisomerism, as these are all examples of chirality in chemistry. One cannot discuss diastereomers without first discussing enantiomers anyway. You could actually merge enantiomer and diastereomer into the stereochemistry article instead, which IMO would make more sense. There is no reason to only merge enantiomer into chirality, as there are many other forms of chirality in chemistry. Endtothemeans (talk) 03:34, 8 June 2008 (UTC)

Perhaps logically that is correct, but only the two articles that I have suggested to merge have large overlaps in terms of their current content. How about the following: move all of the content from here relating to enantiomerism into that article and have this article simply be a short one with links to enantiomer, diastereomer and atropisomerism? TomViza (talk) 16:50, 9 June 2008 (UTC)

This would work. There is no need for an explanation of enantiomers in an article on chirality in chemistry...they can just be linked. Endtothemeans (talk) 02:04, 21 June 2008 (UTC)

General issues

Alterations and restructuring are needed to properly represent use and meaning of the word chirality. Please join the multi-disciplinary discussion on Talk:Chirality. --Cigno 22:15, 15 November 2005 (UTC)

Wrong word?

Surely the word is asymmetry, not dissymmetry. I was also taught that the correct terms were laevorotatory and dextrorotatory. 21:01, 19 December 2005 (UTC)

• • OED. dissymmetry: Symmetry between two objects, disposed in opposite directions, such as the right and left hands or feet, or between crystals alike in all respects, save that their angles lie opposite ways. Bueller 007 (talk) 06:40, 19 November 2008 (UTC)

poorly executed content move

Content of optical isomerism has been moved to chirality (chemistry), and optical isomer is now the redirect. The result is that many links to this article are now disabled. Please consider fixing the links or better revert the process as chirality (chemistry) is not an elegant name for an article. V8rik 21:54, 6 April 2006 (UTC)

"Elegant name"? Encyclopedias are simple, understandable, and concise, but elegant? I think it confuses the layman far more to attempt to understand how optics is related to chirality, than it is to simply explain the concept using the hand example (which is not very clearly explained in the article). I also think a three dimensional image would help greatly (in place of the 2d one that is currently there; it doesn't show the tetrahedral shape of the molecules). Fuzzform 06:06, 14 May 2006 (UTC)

Isotopes

Is it possible to have this property using isotopes? Suppose in the Alanine molecule the H3C methyl group is replaced with Deuterium instead of hydrogen, does this create an optical isomer? —The preceding unsigned comment was added by 12.10.127.58 (talk • contribs) .

In a glycine molecule where the methylene group is CHD instead of CH₂, that carbon is a chiral center, and the molecule has two possible enantiomers. DMacks 20:36, 1 June 2006 (UTC)

Not all L

The article says:

[...] the D/L system remains in common use in certain areas of biochemistry, such as amino acid and carbohydrate chemistry, because it is convenient to have the same chiral label for all of the commonly-occurring structures of a given type of structure in higher organisms. In the D/L system, they are all L;

They are not all L; there are lots of D's. Or do I misunderstand the sentence? There's for example D-Glyceraldehyde 3-phosphate at a prominent position in glycolysis. AxelBoldt 23:57, 22 September 2006 (UTC)

I think this is probably a very poor attempt at pointing out that in the living, human body; the chiral ratio of amino acids is actively shifted to make L-amino acids dominant (90% L, 10% D); and conversely D-monosaccharides are dominant. Only the L-forms of amino acids are active in humans, only the D-forms of monosaccharides are active in humans, so the body keeps that gradient there. After you die, the ratio naturally switches back to 50:50.--KX36 20:07, 3 February 2007 (UTC)

Some dodgy stuff in here

There is an implication that all enantiomers are optically active - which is rubbish. Also the term is asymmetric, not dissymmetric - Look up most major textbooks it will use that term

Arguably the R & S nomenclature is the most important so surely that should be placed ahead of the d/l and D/L paragraphs - although I am saying this as a chemist rather than as a biologist

Stui 194.72.70.114 13:02, 4 October 2006 (UTC)

• OED. dissymmetry: Symmetry between two objects, disposed in opposite directions, such as the right and left hands or feet, or between crystals alike in all respects, save that their angles lie opposite ways. Bueller 007 (talk) 06:40, 19 November 2008 (UTC)

Rule surrounding C

The rule where if a tetrahedrally-bonded C has 4 different substituents, then it is chiral applies to any tetrahedrally-bonded element, although C is the most common example. This is according to my university textbook. Mike.lifeguard 00:07, 6 November 2006 (UTC)

It's true. The article here notes that C is a simple example, and it's the case most wikipedia readers will likely encounter or be likely to recognize or are here to learn about. But actually, it's not even limited to atoms that have 4 bonds, and it's not even limited to atom-centered things at all...see BINAP for example. DMacks 16:43, 6 November 2006 (UTC)

D-L Chirality Notation Error

I changed the content of the article because it was just plain wrong!

It said that after putting the lowest priority group at the back, if the remaining constituents were counterclockwise it was D config. If clockwise L config.

This is wrong!!

If a chiral molecule has a counter-clockwise configuration it is L (corresponding to S in Organic Chemistry) If a chiral molecule has a clockwise configuration it is D (corresponding to R in Organic Chemistry)

Just letting everyone know I fixed that. —The preceding unsigned comment was added by MikeMurko (talk • contribs) 00:19, 3 December 2006 (UTC).

I'm affraid it was right the first time and I changed it back. You can check this one yourself. Find yourself a picture of for example D-Alanine, turn the hydrogen away from the viewer and the order COOH R NH2 is counterclockwise! —The preceding unsigned comment was added by 62.253.240.3 (talk)

Looking at the (claimed to be) L-(S)-alanine image on the alanine page, R is the methyl group, H is in the back, and I see (COOH)-(R)-(NH₂) running counter-clockwise. This also seems to agree with the L-(S) stereochemical assignments on the glyceraldehyde page per the description of the origin of the L/R nomenclature (NH₂ instead of OH, methyl instead of methylcarbinol). DMacks 02:13, 3 May 2007 (UTC)

You are right. Sorry about that!

counter clockwise w. r. to...

suggest adding "counterclockwise as viewed against the direction of propagation" or something similar regarding polarization rotation under the History section, in addition to that in the optical activity naming convention section. Angelafit 06:07, 3 December 2006 (UTC)angelafit

Letter example - huh?

A para in the article says:

By contrast, the operation of superimposition is trivial for a non-chiral mirror image (e.g., the letter "A"). Because letters such as "A" are not three-dimensional, though, no chiral letters exist to demonstrate the contrary.

Doesn't "L" 'demonstrate the contrary'? (i.e., it's chiral.) If that's not what the para is about, it needs fuller explanation. -R. S. Shaw 18:37, 11 March 2007 (UTC)

Superposition vs Superimposition

One or more anonymous users (get a user account!) feel that this article should use superposition and not superimposition to explain chirality. I know that McMurry, March etc. use superimposable but what the heck is the difference between the two!. Is is one of those flammable / inflammable thingies that non-native English speakers always mess up or a UK vs US English difference? Any ideas? V8rik 17:53, 6 November 2007 (UTC)

The plain-English definitions (i.e., Wiktionary) suggest that superposition might be more appropriate than superimposition since we're usually talking about things not images. But the former seems to talk more about arbitrary stacking whereas the latter seems more about having some certain alignment (which is what we care about). And we're looking more for a technical term than a linguistic solution I think? I've only ever heard "superposition" in this context as part of the slow-motion revert war here. DMacks 03:37, 7 November 2007 (UTC)

Hi DMacks, thanks for your comment. I am assuming for now that you would be in favor of the term superimposition. So the IM in imposition stems from IMage? I did not realize that until now. I will wait and see if there are more comments otherwise I switch back the article. V8rik 17:42, 7 November 2007 (UTC)

Yes, I'm in favor of "superimposition" both in my mind and because we can support it with McMurry, Wade, Streitwieser/Heathcock/Kosower, and Morrison & Boyd. I'd actually never noticed the "IM" word-root similarity:) DMacks 17:48, 7 November 2007 (UTC)

• Made a switch back V8rik 17:31, 9 November 2007 (UTC)

Slow motion revert war indeed. IUPAC uses "non-superposable". (IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "enantiomer". doi:10.1351/goldbook.E02069.html) --Rifleman 82 (talk) 06:28, 30 June 2008 (UTC)

Just for the heck of it, here's the Google Books Popularity Contest result: enantiomer superposed, 61 hits; enantiomer superimposed, 322 hits. In my opinion, both are equally valid. I don't know if it is due to regional differences or if it is random, though. --Itub (talk) 09:59, 30 June 2008 (UTC)

• There's no debate. "Superimpose" is flatly wrong. ANY two objects can be "superimposed". "Superimpose" just means "putting one thing on top of another". Further, if you "superimpose" something onto something else, both are typically *still visible*. There is no nuance of "exact fit". "Superpose" is a geometric term and it specifically means "transfer one into the space occupied by the other two show that they coincide". Enantiomers are ***non-superposable*** mirror images of one another. IUPAC is correct. Bueller 007 (talk) 06:29, 19 November 2008 (UTC)

D/L typesetting

I notice that all of the instances of "D" and "L" are wrapped in <small> tags. If they're supposed to be in smallcaps, we should use <span style="font-variant:small-caps"> instead: small-caps. I didn't convert over myself because I'm not certain this is what the small tags were intended to accomplish. Bryan Derksen (talk) 05:38, 23 November 2007 (UTC)

The D and L in this context are indeed intended to be small caps. <small> is heck of a lot easier to type than a longer, er "span" of text. DMacks (talk) 16:34, 24 November 2007 (UTC)

Ibuprofen

Ibuprofen is another example of a chiral molecule. One entantiomer has pain relieving effects while the other is inactive. Also, if I remember correctly, the body can convert the inactive form to the active form, which extends the duration of the pain relieving effect of the drug.

KingHanneman (talk) 04:12, 1 February 2008 (UTC)KingHanneman

Yup. See the "Stereochemistry" section of the Ibuprofen article for more info. DMacks (talk) 10:21, 3 February 2008 (UTC)

Comment on the origin of homochirality

From the article:

"The origin of this homochirality in biology is the subject of much debate. Most scientists believe that Earth life's choice of chirality was purely random, and that if carbon-based life forms exist elsewhere in the universe, their chemistry could theoretically have opposite chirality."

I was under the impression that the weak interaction is often suspected as having a role in the origin of homochirality, based partially on indicative experiments involving crystal growth like those of Compton and Pagni (sorry, I don't have a cite off the top of my head). I realize that it's still very speculative to believe this with regards to amino acids in particular, but I wonder whether it's significant enough to comment on in the article? (chemistry isn't my area, so I cannot say)

Even if the hypothesis involving the weak interaction isn't significant enough to include here, the assertion that "most scientists" believe the origin of Earth-bound life's homochirality to be purely random seems misleading. There are certainly plenty who believe it could be the result of natural physical laws. -- 98.26.182.245 (talk) 22:45, 13 October 2008 (UTC)

Are hands really chiral?

Amputated hands represent a pair of enantiomers. But while still attached to the body, and ignoring our blemishes and the "enantioselective" placement of organs, the hands are not chiral since we are C_s-symmetric. So the analogy to hands is flawed. We are however prochiral. Am I missing something?--Smokefoot (talk) 16:16, 20 December 2008 (UTC)

• agree but analogies will only take you that far. The concept of chirality should be explained on the chirality page itself. As long as you say hands are each others mirror images that is okay. To say (as the article suggests) that a hand is chiral is taking it too far. Are we also homochiral as the heart is always on the left side of the body? V8rik (talk) 20:47, 21 December 2008 (UTC)

Greek IPA /cheir/

The term chirality is derived from the Greek word for hand, χειρ-(/cheir/). I'm know this is improper IPA (which is what one uses inside phonological brackets "/ /"), so I'm guessing that the original editor was simply putting the standard romanization in parentheses. Therefore, I've edited out the brackets. 99.141.180.36 (talk) 02:02, 10 June 2009 (UTC)

"chiral center" vs. "chirality center"

I've seen both, is there any difference? Is it worth mentioning? —Preceding unsigned comment added by 173.250.142.56 (talk) 01:45, 1 February 2011 (UTC)

Superposition vs Superimposition again

I found in the the first two paragraphs of the introduction part of the article an incorrect wording :-"non-superposable mirror image".So I corrected it to "non-superimposable".Superposable has a totally different meaning in physics and mathematics.Please check article on Superposition Principle for verification. — Preceding unsigned comment added by Ichgab (talk • contribs) 07:35, 11 June 2011 (UTC) The correction to superimposable was done by me User Ichgab.I forgot to sign my comment.Sorry for the mistake.Ichgab (talk) 07:47, 11 June 2011 (UTC)

I have undone this change per the WP:RS noted in the #Superposition vs Superimposition discussion earlier on this talk-page. As a chemistry article, IUPAC is more authoritative than physics/math technical meanings in their fields (and your change was not supported by that cite given in the article). I have added a heading...because this was filed under '"chiral center" vs. "chirality center"', it's no wonder nobody else noticed or bothered to respond at the time to your separate issue. I have added an additional IUPAC ref that specifically defines "Superposition" as it is used in chemistry to help clarify its meaning in this field. It's definitely different than the superposition principle, so I have removed the link to that target. DMacks (talk) 13:53, 22 January 2012 (UTC)

Chirality of phosphorus

Should the chirality of phosphorus (as in sarin) be included? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 21:45, 3 August 2011 (UTC)

The article should definitely note the general idea that a lone-pair can be considered a substituent (or at least consume a geometric position like one), and therefore give a stereocenter. The "Chirality of amines" section is a start, but it focuses on the transient nature due to rapid inversion, not the fact that each single state is chiral. Probably best to put the idea of chirality for molecules like RR'RN and RR'RP and RR'SO in the "Stereogenic centers" section (including how to name them R/S, etc.). Then separately can have some commentary on the fact that some chiral molecules can invert under standard conditions (pulling together the conformational-changes from "Stereogenic centers" and the amine-inversion idea). There was a discussion on the science ref-desk within the past month or two about barriers to inversion of P and N centers, I think with some links to other WP articles and/or literature sources. DMacks (talk) 02:45, 4 August 2011 (UTC)

Naming conventions

It states that " it is labeled R (for Rectus, Latin for right), if it decreases in counterclockwise direction, it is S (for Sinister, Latin for left)." That is incorrect. rectus means straight (such as rectus abdominis), right in latin is dexter. Where does the R come from then? — Preceding unsigned comment added by 86.135.11.19 (talk) 14:59, 15 January 2012 (UTC)

• good point, R is from Rectus (straight, correct) the text should be changed V8rik (talk) 22:13, 15 January 2012 (UTC)

In English, "right" can mean "correct", but it can also refer to the side opposite "left". In Latin, "rectus" seems to refer to the former, "dexter" the latter, though "right" is a 100% acceptable translation of both words—the problem is that "right" has multiple meanings. Is this as simple as a very old conflation of terms? Or is "rectus" really an additional word for the side opposite left in Latin (even though "dexter" has that covered)? 70.172.214.70 (talk) 04:58, 23 June 2013 (UTC)

Chiral sugars?

Do all sugars have chirality? Or is it only for monosaccharides? 173.17.169.171 (talk) 08:28, 6 March 2012 (UTC)

Almost any sugar that has at least one stereocenter is chiral. A polysaccharide is simply a polymer of monosaccharides, and forming a polymer does not change the chiral fact of the individual monomers within it. If your left and right gloves are chiral, a shopping cart full of gloves is just a whole lot of chirality. DMacks (talk) 16:21, 6 March 2012 (UTC)

Error in RS section of Naming conventions

Dear Editors,

The article currently states the following in the RS section of the Naming conventions:

If the center is oriented so that the lowest-priority of the four is pointed away from a viewer, the viewer will then see two possibilities: If the priority of the remaining three substituents increases in clockwise direction, it is labeled R (for Rectus, Latin for right), if it increases in counterclockwise direction, it is S (for Sinister, Latin for left).

This disagrees with the standard definition (see, e.g., Voet and Voet).

A suggested correction follows:

If the center is oriented so that the lowest-priority of the four is pointed away from a viewer, the viewer will then see two possibilities: If the priority of the remaining three substituents decreases in a clockwise direction, it is labeled R (for Rectus, Latin for right), if it decreases in a counterclockwise direction, it is S (for Sinister, Latin for left).

Thank you

Mewalloffice (talk) 19:10, 17 April 2012 (UTC)

• Thanks for spotting the error. It is is the result of vandalism (21 March 2012). It is already corrected.

Δ and Λ complexes

User:Rifleman 82 disagrees with my edit, but I do not understand why there should be pictures of both Δ and Λ conformationsisomers. Indeed, if it should, then which design is preferable? Incnis Mrsi (talk) 15:13, 7 March 2013 (UTC)

Why don't you use the following:

• 
  Λ-[Fe(ox)₃]³⁻
• 
  Δ-[Fe(ox)₃]³⁻

Showing both delta and lambda enantiomers highlights how chirality can exist apart from tetrahedral carbon compounds, the latter of which, is the most common. --Rifleman 82 (talk) 15:23, 7 March 2013 (UTC)

(edit conflict) "Stereoisomers" not "conformations". But anyway, the whole point of this article is to discuss and illustrate the idea of chirality, and especially the differences among stereoisomers. Only having a picture of one possibility and then saying "and there's another" does not help anyone who does not already understand the key aspect of the difference or to illustrate the quick definition of the "other" symbol. But I also think File:Énantiomères octaèdriques.jpg might be too oversimplified, since it doesn't help if you don't really understand the molecules being represented. Maybe the [Fe(ox)₃]^3– 3D-balls images from Complex (chemistry)#Optical isomerism would be better here? DMacks (talk) 15:28, 7 March 2013 (UTC)

I do not object against any picture but JPEG, and any changes but destruction of typography fixes and wikification already made by me. Incnis Mrsi (talk) 15:56, 7 March 2013 (UTC)

We have indeed been moving away from JPEG to PNG or SVG images, but JPEG images should not be removed unless an equally good replacement is available. --Rifleman 82 (talk) 16:10, 7 March 2013 (UTC)

And agree with this statement too. A JPEG is better than nothing and better than an image that doesn't illustrate the appropriate/relevant content. File format is *not* the most important aspect of an article. DMacks (talk) 16:29, 7 March 2013 (UTC)

What could illustrate this downscaled heap of muck? Incompetence of the creator and low quality of contributions of the user who placed it here, IMHO. I do not think that this loathsome image could really help to understand the 3D structure of complexes even accurately remade in SVG but with exactly same graphical features. Incnis Mrsi (talk) 16:51, 7 March 2013 (UTC)

There are two equilateral triangles in this graphic (either enantiomer), and they mark the face formed by three vertexes of the octahedral metal complex. The round lines join two vertices together; they represent a chelating ligand. By seeing how the "propeller" rotates, you can assign delta or lambda symmetry to the compound. Some chemists prefer such a representation that omits the central metal atom, but I'm not a fan. --Rifleman 82 (talk) 17:09, 7 March 2013 (UTC)

Chiral molecules with different properties?

I'm curious as to if there are chemicals with different melting points, or such, when flipped. I mean it doesn't seem like there would be according to simple valance electron theory, but then again, He3/He4 are very different beasts when isolated (spin-related cause).

I'm curious as to if some trios of atoms have a preferred relative orientation. Think of particle physics and the layout of the brain where globally it seems they're reflections but locally they might not be. They turn out to only be good approximations.71.196.246.113 (talk) 19:21, 9 March 2013 (UTC)

In their pure forms and when not mixed with other chiral compounds, two enantiomers have the same melting point and such as each other because whatever their preferred relative orientation, it's a relative orientation. The mirror image would have the same relative orientation, just in the opposite direction. Diastereomers could be as different as any two unrelated compounds (except for same molecular weight) precisely because of different relative orientations. DMacks (talk) 20:55, 9 March 2013 (UTC)

I do not think that something like this is possible under typical circumstances because both electromagnetic and nuclear force are P-invariant. Though, it is perfectly possible under the same external influence which is not P-invariant. I can easily imagine two chiral isomers which have different properties if irradiated by the same circularly-polarized light. Or, say, under superposed electric and magnetic fields which are not perpendicular – parities of E and H fields are positive and negative respectively. Incnis Mrsi (talk) 21:09, 9 March 2013 (UTC)

Yes, I was thinking of the magnetic and spin properties. A neat (and lethal) thing is that H2 has biologically different effects than the H1 that is in most water molecules. For microbes, it slows them down to about half speed (twice as much energy needed to move the same number of hydrogen atoms?) but for animals... does a lot more than just slow us. Another thing that seems odd at first sight is that helium actually becomes toxic at high enough depths. I think it was related to neuron connections? I actually doubt too many if any molecules will have detectable differences in melting points but I'm willing to bet that muons or something will react differently. μ+SR and μ-SR (Muon/Mu Meson/Mu-Electron bombardment) is an interesting technology. Not everything can be done at places like the CERN LHC. We need smaller-hadron colliders, too!  ;) Too bad there's no practical way to do Muon-chemistry in electronics. I could see a lot of potential applications. 71.196.246.113 (talk) 19:45, 10 March 2013 (UTC)

• Deuterium is toxic because it has different chemistry, it's C-H bonds are slightly stronger than those of normal hydrogen and enzymes have a very hard time dealing with that (see Heavy water. I think helium toxicity (HPNS) is caused by it building up in the tissues to such a point that it becomes disruptive (similar to Nitrogen narcosis).Project Osprey (talk) 20:18, 10 March 2013 (UTC)