Talk:Zwitterion

Definition concern
I don't know about the definition of zwitterion. Other sources claim the definition is an ion with both a negative and positive formal charge somewhere in the structure. I've classified p-Azoxyanisole as a zwitterion based on this definition.

--Edsanville 21:07, 2 Jun 2004 (UTC)

Quinonoid zwitterion
Quinonoid zwitterion is not a typical zwitterion it should therefore not rank with the typical zwitterions rikXL 15:24, 25 Jun 2005 (UTC)

How's that, then? Ed Sanville 19:32, 25 Jun 2005 (UTC)

Zwitterion definition
I am of the understanding that zwitterion refers only to the form of a molecule with one acidic and and one basic group where positive and negative formal charges are present at the same time, such that the net charge is zero. Therefore, a molecule could only be a zwitterion at its isoelectric point. At other pHs it would be anionic or cationic. The way the article is written now makes it seem like any amphoteric molecule is a zwitterion, when it would only be so at a particular pH, and then only if it had one acidic and one basic moiety. I want to make sure this is an accepted definition before I dive in and rewrite the page; any opinions? Porkchopmcmoose 02:05, 30 March 2006 (UTC)

A buffer always contains a weak acid and conjugate base in equilibrium. A zwitterion on its own could not function as a buffer. e.g CH2(COO-)NH3+, on its own has no buffering ability, but mixed with CH2(COOH)NH3+ or CH2(COO-)NH2, can act as a buffer.

Two concerns: DMacks 14:14, 14 March 2007 (UTC)
 * 1) Just because a molecule that has acidic and basic components doesn't mean they both ionize to create a zwitterion. Creating charge or adding/removing proton from some position might destabilize the molecule in some way--for example, destroying aromaticity in 2-pyrrole carboxylic acid. At least in solid state, o-anthranilic acid is a 1:1 mixture of zwitterionic and non-ionic forms.
 * 2) There are zwitterions that are not due to (effectively) intramolecular acid/base chemistry and equilibria, so juggling pH or other titration/solution games has no effect. Nitromethane and acetonitrile N-oxide are some simple cases.


 * I always understood a zwitterion was any species with positive and negative charged groups at a given pH, I didn't appreciate that it had to be only 1 of each. Are you sure this is technically correct? What about something with 2 positive charges and 2 negatives, is this a zwitterion? Aaadddaaammm 23:19, 31 March 2007 (UTC)
 * OK, after consultation of a textbook, I'll agree that it has to have no net charge, but can it have many charged groups all cancelling each other out? Ie. is a protein at its pI a zwitterion? Aaadddaaammm 23:22, 31 March 2007 (UTC)

Pronunciation
How should the word "zwitterion" be pronounced?

83.30.188.212 15:56, 30 August 2007 (UTC)


 * For what it's worth, see:
 * https://en.wiktionary.org/wiki/zwitterion /ˈtswɪtəɹ.aɪən/ and (with audio sample) https://de.wiktionary.org/wiki/Zwitter


 * Simon de Danser (talk) 16:40, 25 May 2020 (UTC)

Dipolar compounds
I added dipolar compounds, but I am not quite sure about the interpretation.

IUPAC Gold Book uses very similar definitions, but it will not be without a reason to use different lemmas. In contrast to ampholytes that are redirected to zwitterionic compounds, suggesting them to be synonym.

Zwitterionic compounds:

"Neutral compounds having formal unit electrical charges of opposite sign."

Dipolar compounds:

"Electrically neutral molecules carrying a positive and a negative charge in one of their major canonical descriptions."

See also: IUPAC Preferred IUPAC Names, Provisional recommendations; pp. 56-71

A more explicit explanation of the difference is desirable. Is there a specialist?--Wickey-nl (talk) 14:20, 8 June 2010 (UTC)
 * Dipolar compounds are not ions and therefore they cannot be Zwitterions, its not a good idea to put them in the same article.--Azaline Gomberg —Preceding undated comment added 09:28, 17 December 2010 (UTC).
 * I removed the statement because it is leading us off-topic or is redundant to previous sentence. However, http://goldbook.iupac.org/D01753.html defines "dipolar compounds" as "Electrically neutral molecules carrying a positive and a negative charge in one of their major canonical descriptions", and even gives examples that do not have the charges on adjacent positions (cf. some scientists' concern about usage). Can you give us a specific compound you believe to be dipolar but not zwitterionic? One possible confusion is that the definition involves dipole, which according to the technical definition in this case appears to be only actual formal charges, rather than also partial charges in the more general bond polarity sense. DMacks (talk) 09:41, 17 December 2010 (UTC)
 * The word dipolar compound is used in the context of Cycloadditions for example Ozone in Ozonolysis, whereas Zwitterion is mainly used in the context of Aminoacids at their isoelectric point. --Azaline Gomberg —Preceding undated comment added 10:08, 17 December 2010 (UTC).
 * That's true for common usage (different terms for different contexts, especially when trying to highlight certain reactivity features), but the definitions as written do not seem to make as clear a distinction. For example, O––O+=O looks just as "ionic" as O––N+(CH3)CH3 (which IUPAC lists as an example of a zwitterion).
 * But Ozone has two canonical forms, the negative charge is delocalized on the first and the last O, thats the difference. --Azaline Gomberg —Preceding unsigned comment added by 81.63.104.44 (talk) 10:29, 17 December 2010 (UTC)
 * GoldBook def of "dipolar compound" states "In most dipolar compounds the charges are delocalized; however the term is also applied to species where this is not the case." Note that I'm not disagreeing with common usage, and I already did remove the statement about dipoles from the article because it's misleading by common usage (even if technically correct). DMacks (talk) 10:37, 17 December 2010 (UTC)
 * I would have prefered two different articles for dipolar compounds and Zwitterions. But thanks for the discussion. --Azaline Gomberg (talk) 11:26, 17 December 2010 (UTC)
 * Depending on how much can be told about dipolar compounds. Alternatively, the difference could be explained in a separate section.--Wickey-nl (talk) 11:52, 17 December 2010 (UTC)


 * The resonance structures of ozone represent it's hybridized bonds nature, zwitterions are not hybridized but intermolecular proton exchange causes both isomers (see below).
 * Simon de Danser (talk) 18:12, 25 May 2020 (UTC)

We do have an articles specifically about 1,3-dipole structures and the 1,3-dipolar cycloaddition reaction. Both seem a bit sparse. DMacks (talk) 12:34, 17 December 2010 (UTC)
 * I had seen them, but there has to be an overarching article. I do not feel to be the person to do this.--Wickey-nl (talk) 16:56, 17 December 2010 (UTC)

I moved one sentence to the second paragraph, because 1,2-dipolar compounds and 1,3-dipolar compounds are not really examples, I would say these are rather subclasses. A further possibility would be to move the sentence to the end of the article and additionally give some examples for both kinds of dipolar compounds. But I would not do that because I still think that this article should not include to much about dipolar compounds. But I have to admit that the new version underlines also the difference of the definitions and is much better structured. --Azaline Gomberg (talk) 19:24, 19 December 2010 (UTC)

definitions
I think, the problem is that there are not clear and generally accepted definitions (or are there?). Zwitterions and dipolar compounds both are neutral and have positive and negative charge. Therefore the article could be named "(neutral) polar compounds". Zwitterions can be seen as dipolar compounds, unless dipolar not only means "with positive and negative charge", but also that the compound has only two charged centers (don't know if all dipolar compounds have only two charged centers). There are zwitterions with more than two; e.g. we have amino acids with multiple amino's.

A useful distinction can be the presence of both acidic and basic groups (ampholytes). Some people consider zwitterion and ampholyte synonym (see Isoelectric point), but ampholytes are only zwitterions at their isoelectric point. By the way, I redirected ampholyte to Amphoterism, originally with this title.--Wickey-nl (talk) 16:53, 20 December 2010 (UTC)


 * There are clear and different definitions. Dipolar compounds can have zwitterionic canonical forms. Dipolar compounds can also have non zwitterionic canonical forms. Zwitterions can not have non zwitterionic canonical forms. Dipolar compounds react in dipolar Cycloadditions.
 * The article should not be named "neutral polar compound" because polar compounds (for example water) are not necessarily dipolar or zwitterionic. I think you should not change or rename the article to quickly. Haste makes waste. Its better to discuss it first. Regards --Azaline Gomberg (talk) 18:42, 20 December 2010 (UTC)


 * Don't worry, the name was for discussion only. Definitions are arbitrary, by definition. The difference is not so simple as you suggest. Do dipolar compounds without delocalized charges have a canonical form (a resonance nature)? Are zwitterions and zwitterions the same? Therefore I mentioned the ampholyte example. Do 1,2- and 1,3-dipolar compounds have an isoelectric point? Could be a difference.--Wickey-nl (talk) 11:39, 21 December 2010 (UTC)

The key difference is that in dipolar compounds the charges are delocalized. I see no evidence from the Gold Book that both topics should belong in the same page V8rik (talk) 21:20, 21 December 2010 (UTC)
 * Any reference to dipolar compound will simply have to go. From the Gold Book
 * zwitterionic compounds/zwitterions Neutral compounds having formal unit electrical charges of opposite sign. Some chemists restrict the term to compounds with the charges on non-adjacent atoms. Sometimes referred to as inner salts, dipolar ions (a misnomer).
 * dipolar compounds: Electrically neutral molecules carrying a positive and a negative charge in one of their major canonical descriptions. In most dipolar compounds the charges are delocalized No mention of zwitterions.


 * For splitting the article you need two conditions. 1. Dipolar compounds are not zwitterions 2. Zwitterions are not dipolar compounds. The first condition is partly not true; the second one in fact not at all, if you take the term literally. Zwitterions have two poles. In fact, you can also call water a dipolar compound! The only difference is that it is a partial charge, but it has an electric dipole moment. So the suggested name "neutral polar compound" is not so bad. The title Zwitterion is not good at all, because it is a misnomer. And again the question, Do dipolar compounds without delocalized charges have a canonical form? The Gold Book definition does not give examples.--Wickey-nl (talk) 12:55, 22 December 2010 (UTC)


 * If want to make a lasting impact on high profile articles like this one I really suggest you get access to some more literature than just the Gold Book. Your arguments do not convince me. You are confusing resonance and polarity V8rik (talk) 18:11, 22 December 2010 (UTC)


 * No, I am not. For splitting the article, you need more arguments. Zwitterions and dipolar compounds are polar too. Adding compounds with partial charge is more logical, if it is a difference at all. And if it is a difference, it should be mentioned and explained here.
 * H+-O−-H ↔  H-O−-H+
 * Voila, a 1,3-dipolar compound, even nearly meeting the Gold Book definition. Even if you do not agree with this, I will not repeat my remarks above.--Wickey-nl (talk) 12:17, 23 December 2010 (UTC)

Isocyanide is not a zwitterion to most chemists
The article shows the resonance structures for an isocyanide, but no (or few) self-respecting organic chemist would call that a zwitterion. In fact they would view RNC as a non-example. So I was thinking of replacing this image with a non-controversial example such as glycine at neutral pH.--Smokefoot (talk) 00:08, 24 December 2010 (UTC)


 * I agree and I already stated above, that everything in the article about dipolar compounds does not belong in this article. Regards --Azaline Gomberg (talk) 08:40, 24 December 2010 (UTC)


 * Smokefoot, how do, as a self-respecting organic chemist, define zwitterions and dipolar compounds?--Wickey-nl (talk) 09:53, 24 December 2010 (UTC)
 * Well I was mainly suggesting that we insert glycine while the debate is ongoing. Everyone agrees glycine is an unambiguous zwitterion. (Browser problem).

Related to the debate, here are my opinions: Resonance structures are not zwitterions. In fact resonance structures are not even real, just a concept, so it does not matter what we call them, and this article is about a class of real compounds. At least that is how I see the world.

I also recommend that we remove the image of resonance structures of isocyanide. --Smokefoot (talk) 00:23, 25 December 2010 (UTC)


 * I will never call myselve an expert about dipolar compounds and you will certainly know more about it, but as I interpret the Gold Book definition of dipolar compounds it are compounds that can be pictured as structures that meet the definition of zwitterions. And even the term indicates that. Acetonitrile may be a more concrete example, but surely many other can be found. Surely many definitions are used, so one will not be enough. But still I did not see your definitions.--Wickey-nl (talk) 12:41, 25 December 2010 (UTC)


 * This IUPAC document is clear (see page 56→). 1,2- and 1,3-dipolar compounds are called zwitterionic compounds and the zwitter-form is mostly even preferred for naming. So, I consider them as a class of zwitterions. A separate article about dipolar compounds is desirable as well, but cannot ban them from this page. And actually, I don't see why a water molecule would not be a zwitterion.--Wickey-nl (talk) 14:50, 26 December 2010 (UTC)


 * Water is not a zwitterion. The formula you drew above is wrong. If the H would have a positive charge, it would not bind to the oxygen. As long as the hydrogen has a binding, it has a valence electron and is therefore not positiv. Do you understand it now? The polarity in the water molecule is only based on the difference in electronegativity between H and O.
 * I have read your document. I still think we should seperate it. Simply because it is confusing and its not common usage. The term dipolar compounds is used for compounds reacting in dipolar cycloadditions and zwitterion is used for describing aminoacids. If a wikipedian wants to read something about either of the two topics, he has no need for both definitions. Regards --Azaline Gomberg (talk) 21:44, 26 December 2010 (UTC)


 * the IUPAC report only states that in the report dipolar compounds are discussed in the same section as zwitterionic compounds, right after the cations but before the radical ions.The report is irrelevant V8rik (talk) 20:16, 27 December 2010 (UTC)
 * I support V8rik, an established expert on organic chemistry and to Gomberg who makes a good case. Water being zwitterionic, wha?--Smokefoot (talk) 20:53, 27 December 2010 (UTC)


 * The water molecule fully meet the IUPAC definition. And H+-O−-H ↔  H-O−-H+ is wrong?  A resonance formula does not reflect the exact electronic configuration.  And consider the trihydrogen cation . Here, also a proton is bound without a valence electron.--Wickey-nl (talk) 17:20, 28 December 2010 (UTC)

Article revised
It is clear from the discussion above that a consensus has been reached amongst experienced editors. I add my voice to emphatically deny that dipolar compounds have anything to do with zwitterions. The article has been revised accordingly.

References to isoelectronic point (pI) have been removed because pI says nothing about the zwitterion molecule equilibrium. The isoelectric point for an amino acid, AH, occurs when [A-] = [AH+]. I've added a section to acid dissociation constant which makes this clear. Dubious examples, including sulphonates that are not normally able to be protonated, have also been removed. Petergans (talk) 15:03, 1 January 2011 (UTC)


 * In your definition, dipolar compounds are not zwitterions.


 * Why are in this IUPAC document zwitterions and dipolar compounds put into the same paragraph? Why are dipolar compounds called zwitterionic compounds if they are not zwitterions? Why are there zwitterions without proton transfer? What about Nitrones and betaines? Which source excludes dipolar compounds from zwitterionic compounds? Do dipolar compounds have formal charges and zwitterions not? Are charges in zwitterions real and in dipolar compounds not? Are zwitterions dipoles and dipolar compounds not? Has nitrogen in amino acids another sort of charge than in dipolar compounds? --Wickey-nl (talk) 15:16, 3 January 2011 (UTC)
 * None of your questions above constitutes a definition. The definition of a zwitterion states that it carries real electrical charges; a dipolar compound is one for which a canonical form may be written with formal charges. The consensus between user:Azaline Gomberg, user:v8rik, user:smokefoot and myself is that one can say that dipolar canonical forms are like zwitterions, but that does not mean that they are such. I may add that formal charges are an artefact of valence bond theory and are not used at all in molecular orbital theory of electronic structures.
 * You are the only dissenter and your arguments have been repeatedly descibed as "unconvincing". This discussion should therefore now be closed. Petergans (talk) 17:29, 3 January 2011 (UTC)


 * Poor arguments and lack of arguments gives poor discussions. Users/pseudo-scientists can easily promote each other to experts.--Wickey-nl (talk) 12:04, 5 January 2011 (UTC)

Edit
I removed this: It is characteristic of zwitterions that an electrically charged atom (H+ in this case) is transferred from one part of the molecule to another. It's not necessarily true - check out the structure of the betaine.

Nonsense
The article contains nonsense without sources.

"Though amine oxides are often written as ≡N+O-, they are not zwitterions as they can also be written as uncharged molecules with a dative covalent bond"

Wrong. http://goldbook.iupac.org/A00273.html
 * This source does not call an amine oxide a zwitterion.Petergans (talk) 18:15, 4 March 2011 (UTC)
 * I'm not quite sure which bit you think is wrong, but I think there should be a single covalent bond between the N and the O (as well as the triple bond and the charges). Chris (talk) 21:44, 4 March 2011 (UTC)

"A "dipolar compound", such as a 1,2-dipole or a 1,3-dipole is not a zwitterion."

Wrong. Zwitterion is a general term for any neutral molecule with a positive and a negative electrical charge (by incompetent edits the definition is extended to non-neutral molecules now). See: 1,3-zwitterion; 1,3-zwitterion; 1,4-zwitterion; quinoline–DMAD zwitterion; Cycloaddition mechanism; Phosphorus-containing 1,3-zwitterions; Criegee zwitterion (Criegee zwitterion).

"The distinction lies in the fact that there are formal charges, not electrical charges, on atoms."

Wrong. Amino acids as well as 1,2- and 1,3-dipolars have formal charges (and real charges).

--Wickey-nl (talk) 15:49, 4 March 2011 (UTC)


 * Phrases such as "nonsense", "wrong" and "incompetent edits" are not acceptable.


 * Some of the references cited are not about 1,2-dipole or 1,3-dipoles as described in their linked WP articles. Take the first example 1,3-zwitterion This is not a 1,3-dipole, but is a genuine zwitterion because the boron atom is 4-coordinate, so must carry a negative charge. Petergans (talk) 18:15, 4 March 2011 (UTC)
 * It has a negative charge. Give a source saying it is not a 1,3-dipole. This is an example of mixing the terms zwitterion and 1,3-dipole. Other examples also show the general usage of the term zwitterion--Wickey-nl (talk) 12:03, 5 March 2011 (UTC)


 * The Gold book says about dipolar molecules: "Electrically neutral molecules carrying a positive and a negative charge in one of their major canonical descriptions". Note that it does not say "ALL of their canonical forms". The effect of this is that there is less than a complete positive charge on any given atom - that's what makes it dipolar. Zwitterions have positive and negative charges in ALL of their canonical descriptions, meaning that there is separation of a unit electrical charge. There's no way to draw them without the charges. Thus, because it also says that zwitterions have separation of a unit charge, dipolar compounds are not zwitterions. QED. Chris (talk) 13:27, 5 March 2011 (UTC)
 * My answer below.

^^^^^^^^^^^^^^^^^^^^^^^


 * Wickey-nl: Since you're so fond of the gold book, look at . It says Zwitterions are "Neutral compounds having formal unit electrical charges of opposite sign". The important word there is "unit", and I'm suprised it hasn't come up in the previous discussions above. It means one. A complete charge, not a dipole, which is how zwitterions differ from dipoles. Furthermore, it also says "Some chemists restrict the term to compounds with the charges on non-adjacent atoms", which would rule out amine oxides and nitrones and Criegee Zwitterions, but it does not say that this is agreed upon. Therefore, I propose that we remove this bit from the article, or at least rewrite it with this reservation. Chris (talk) 21:44, 4 March 2011 (UTC) again.
 * Regarding unit charges, this is exactly the point I was making when referring to the distinction between electrical and formal charges.
 * The latest revision is not helpful because it confuses formal charges on an amine oxide with unit charges. I regret to have to repeat that the formal charges on an amine oxide are an artefact of Valence Bond theory, quite distinct from, for example, the (unit) electrical charge on a quaternary nitrogen atom. Also they are completely absent from a Molecular Orbital bonding description. I have tried again to clarify the wording in the light of these comments. Petergans (talk) 10:46, 5 March 2011 (UTC)
 * Ah, I see your point now. It's quite subtle though - I don't think that people will know that "electrical charges" means unit charges and the distinction from formal charges so you might try to clarify that again(!). Also, I have removed the emphasis on having these charges on atoms, because they are often delocalised. You and I both know that in that the trimethylglycine shown the negative charge is delocalised over the carboxylate, not localised on one of the O atoms. I made some more changes to this effect. Regards, Chris (talk) 11:20, 5 March 2011 (UTC)
 * Another source of confusion, between electrical charges as written in a chemical formula and actual charge density on atoms. For example, the ammonium ion carries one positive charge and is written as NH4+, but in reality the charge density varies over the whole molecule. Delocalization is always present and does not impinge on the definition of zwitterion. Petergans (talk) 17:51, 5 March 2011 (UTC)


 * Gold book definitions are not always unambiguous and especially this is not a strong one. It does not say there has to be exactly one charged major canonical description; in fact there are examples with more. It also does not say they are not zwitterions. Note that zwitterions also are dipolar.--Wickey-nl (talk) 14:32, 5 March 2011 (UTC)

The Gold Book is often simply the only online reference. I certainly do not say they are always good. I think they had some trouble with making an artificial distinction between between zwitterions and dipolar compounds. Clinging to that idea leads to spasmodic adaptations, such as "they tend not to be regarded as zwitterions because they can also be written as uncharged molecules with a dative covalent bond". This is not based on reliable sources.

Nitrogen in amino acids will not have a full unit positive charge, because it will interact with all other atoms, but it has a full unit formal charge. On the other hand, nitrogen in "dipolars" also has a full unit formal charge.

Apart from the fact that the Gold Book does not say that dipolar compounds are not zwitterions and neither the reverse, we can see the general usage in literature, including the Criegee zwitterion. So I propose to distinct:
 * Zwitterions with proton transfer
 * Zwitterions with delocalized electrons
 * Other zwitterions

--Wickey-nl (talk) 12:03, 5 March 2011 (UTC)

This discussion is going nowhere. I am removing zwitterion from my watch list. Petergans (talk) 17:55, 5 March 2011 (UTC)

Discussion continuing
Seems like you're getting into an edit war with your fellow editors, Wickey-nl. Don't keep reverting to your version of the article. Until you have unambiguous support on this talk page to make changes, do not edit this article.

Ben (talk) 12:08, 11 March 2011 (UTC)


 * I have not seen a valid argument for the POV that dipolar compounds are not zwitterions. The Gold Book says:


 * "Some chemists restrict the term to compounds with the charges on non-adjacent atoms."


 * That sounds like: Most chemists include them. Otherwise, it would not make sense in the definition. How different are amino acids, betaines and amine oxides with respect to charges and dipole moments?--Wickey-nl (talk) 12:43, 11 March 2011 (UTC)


 * They are very different, and that is where you reveal your ignorance. In a betaine, an electron is transferred from a nitrogen based atomic orbital to a MO based somewhere else on the molecule. In amine oxides and so forth, the electron is transferred from the nitrogen atomic orbital to a molecular orbital that encompasses both the nitrogen and the oxygen atom. It is not completely lost from the N atom, because the MO has some electron density there. The N atom does not carry a complete positive charge and is not ionic. I am reverting your changes again. Before you change them back I suggest you find a reputable source that unambiguously states that amine oxides, nitrones and anything else you want to put in are zwitterions. Chris (talk) 16:46, 11 March 2011 (UTC)

Wickey-nl, I think you need to take a more dispassionate approach. Don't rely on the Gold Book. Take a broad view, see whether on the whole, in the literature, chemists consider dipolar compounds to be a subset of zwitterions or not. Consult several (many) authoritative sources, see if they agree. Do not go out specifically looking for sources that agree with your belief. Try and quantify how much of the literature agrees with you and how much does not. Not an easy task, but give it a shot. Because unless you present a compelling case, other editors will tend to think you're just pushing some sort of agenda.

Ben (talk) 17:04, 11 March 2011 (UTC)


 * chemists consider dipolar compounds to be a subset of zwitterions or not. That is exactly the point. I am not interested to put in my POV. If the term is not unambiguous, different opinions may be present. I meant, all compounds are neutral, have positive and negative charge, have a dipole moment and even have the same IUPAC nomenclature (important or not). I gave a number of refs with divers examples. Chris did not give sources that legitimate restriction to one POV.--Wickey-nl (talk) 18:14, 11 March 2011 (UTC)

The onus is on you to prove your case. Chris is not required to give a source. He also made the point that despite the similarities between zwitterions and dipoles that you mention, dipoles are fundamentally different because their positive and negative charges are linked electronically (i.e. linked via an orbital).

Ben (talk) 18:51, 11 March 2011 (UTC)


 * I would also point out that just because the gold book does not explicitly rule something out, that something is not automatically true. Find me a reputable source that says that 1,3-dipoles are zwitterions, or vice-versa. Chris (talk) 19:58, 11 March 2011 (UTC)

Pitty that this non-discussion is still based on bluff and and poor arguments. The suggestions of a "sort of agenda" and the only relevant reference in the article, from the generally accepted Gold Book, to be unreliable are the most strong arguments so far.

A meaningless cry about MO's is not convincing. If it were so simple, a definition without dipolar compounds could easily be made. Zwitterion is not about the question from where to where charges go. It is simply about "Neutral compounds having formal unit electrical charges of opposite sign".

In amino acids, three hydrogens and a carbon are sharing electrons with N; in trimethylamine oxide, three carbons and an oxygen are sharing electrons with N. In both cases N donates a lone pair.

You ignore the trimethylamine oxide example in the Gold Book definition. Even in your manipulated definition ylides, etc. are not ruled out (the silly addition "(n.b. not dipoles)" we can ignore, as amino acids are dipoles. The difference with my version is that you change the Gold Book definition into your POV.--Wickey-nl (talk) 11:18, 12 March 2011 (UTC)

Reset discussion, focus on reliable sources
This discussion is not getting anywhere because we're attacking each other's logic (right or wrong, it's OR) rather than doing a literature review.

Wickey-nl, I see you've provided links to two books and several journal articles above. Good start, but not as comprehensive a survey as we need for this apparently contentious issue.

The fact that the Gold Book bothers to mention that "Some chemists restrict the term [zwitterion] to compounds with the charges on non-adjacent atoms" suggests it is a view held by a significant proportion of chemists. On its own, the term "some chemists" could in principle mean as few as two. But common sense suggests the Gold Book's authors wouldn't include the "non-adjacent" variant definition unless a significant minority of chemists used it.

So let's see what major textbooks and researchers say on the issue. I'll add to the following table as I check more sources. Definition 1 means the view that dipolar compounds are a kind of zwitterion. Definition 2 refers to the view that dipolar compounds are not zwitterions.

Here are a few Web of Science searches to help us out:


 * topic = 1,3-dipole AND zwitterion
 * topic = dipolar AND zwitterion; page 1 of 2
 * topic = dipolar AND zwitterion; page 2 of 2

Ben (talk) 14:37, 12 March 2011 (UTC)


 * OK, this is the way to explore knowledge. Because I don't have the disposal of a library, I asked for an expert, not for non-experts who only put their POV into the article and overrule in a coalition.


 * If the Gold Book states "Some chemists restrict the term", I assume a substantial number, as reflected in my edit. Not the same as Some chemists do not restrict the term, though. In the last case, the majority would restrict the term (thus say dipolar compounds are not zwitterions). Having said that, I emphesize that other sources are important. If there are not general definitions, we have to do with "ad hoc" citations.


 * E.g. Braida, 2010. I do not have the full text, but added it to your table. Heuschmann, 2003. Zwitterion with delocalized electrons. 1,4-Dipole? not sure. Machiguchi, 2003. 1,4-Zwitterion with delocalized electrons.--Wickey-nl (talk) 12:33, 13 March 2011 (UTC)

Good, thanks, this is more productive now.

You asked for an expert, and you got three. Chris, Smokefoot and Petergans are all professional chemists. They have PhDs and have taught in universities.

Or do you mean you want the world expert on zwitterion and dipole nomenclature?

Ben (talk) 13:44, 13 March 2011 (UTC)


 * Not recognizable experts in their edits, but no one can be an expert in everything. A real scientist would not rewrite the article to obscure an important view, without references. He also would consider his view, if there are reasonable arguments. Not ignore arguments. Earlier I suggested to include several definitions, which is ignored. On the contrary, Petergans manipulated the Gold Book definition and put in his own. But I am open for reviews about other sources, as far as they are sincerely.--Wickey-nl (talk) 16:27, 14 March 2011 (UTC)

They're just using their professional experience to guide their editing. Unless you're an expert yourself, you won't be able to determine whether another editor is an expert just by looking at their edits. These guys feel comfortable interpreting the Gold Book flexibly or ignoring it at times, because they are experts and the Gold Book is a general sort of thing, not to be trusted above all else. Don't say they're not real scientists, because they are. If you're paid by a university to do scientific research and publish it in high-quality, high-impact peer-reviewed journals, you're definitely a scientist. I trust their judgement more than your reliance on synthesis and inference from a handful of source.

Nonetheless, it's obviously better if reliable sources can be cited to support the definitions we give in our articles. That is what I am trying to find.

p.s. At the moment, this article is looking like a good candidate for Lamest edit wars.

Ben (talk) 17:30, 14 March 2011 (UTC)


 * Let us go back to facts. First, I don't have any connection with IUPAC and because Gold Book definitions are very general and sometimes ambiguous they are suitable for supporting statements rather than for basic source. But if there are no other sources, they may be used. While 1,20 meter is still a measurement in units meter, formal electrical charges are always counted in full units, by definition. There is also no reason at all to distinct zwitterions with full and with partial electron separation, and I have not seen an example of that, in terms of definition. Nor there is a reason to distinct delocalized and non-delocalized electrons.


 * As you noticed well, the question is wether or not dipolar compounds are zwitterions. According to the Gold Book definition they are and there is nothing wrong with supporting this with citations in scientific journals.--Wickey-nl (talk) 11:20, 15 March 2011 (UTC)

"There is also no reason at all to distinct zwitterions with full and with partial electron separation, and I have not seen an example of that, in terms of definition. Nor there is a reason to distinct delocalized and non-delocalized electrons." - You want to focus on facts, but these are not facts. They are your opinion.

My opinion differs: I think it is often appropriate to make a distinction between delocalised and localised electrons.

However, neither your opinion nor mine matters to this article. The article needs to take a dispassionate, neutral view. You and I both know that.

Searching for literature/textbook examples of the various common definitions of "zwitterion" and of "dipolar compound" is a better use of our time than debating the issue with our own reasoning and biases. Better still, we spend the time adding new content to this and other articles. I think the best thing to do is say what the Gold Book says: a certain proportion of chemists do exclude dipolar compounds from their definition of zwitterion. Then we can forget all about this tedious debate about a minor point.

Ben (talk) 19:30, 15 March 2011 (UTC)
 * While you may call it an opinion wether or not dipolar compounds are zwitterions, I did not say the distinction between delocalised and localised electrons is unimportant. That would be foolish. The question is not a minor point, otherwise it wasn't worth a debate. Moreover, the question is about how sources are used and misused. --Wickey-nl (talk) 13:58, 16 March 2011 (UTC)

You specifically said "Nor there is a reason to distinct delocalized and non-delocalized electrons". In response, I said "I think it is often appropriate to make a distinction between delocalised and localised electrons". Now you reply "I did not say the distinction between delocalised and localised electrons is unimportant". So which is it? I'm confused.

I think the whole issue of zwitterion/dipolar compound IS a minor point, and wasn't worth a debate. This debate has been a waste of time. You're the only one who thinks it's a big deal. I'm involved because I don't like editors throwing their weight around, pushing a particular view point too hard. I'm not involved because I care very much about definitions.

You keep accusing other editors of misusing sources, but they're actually just using common sense and experience alongside sources.

Ben (talk) 22:37, 16 March 2011 (UTC)


 * Read my edits in the context they are written. As far as I can judge, zwitterion is just a loosy term for a neutral compound with positive and negative charges. In this respect, delocalization of electrons is not relevant. In this respect, the whole article is not relevant.


 * If you care about definitions, you should be concerned about the current article. Yes, definitions are misused, because the zwitterion definition is cited selective and the dipolar compound definition is used to "prove" that they are not zwitterions. As long as my arguments are not addressed, the "superior experts" do not have right to speak.--Wickey-nl (talk) 15:45, 17 March 2011 (UTC)

I do not care about definitions. Understanding and explaining the actual chemistry is much more important.

Experts do have a right to speak, and a right to ignore your concerns. Let's just leave this article alone now.

Ben (talk) 16:01, 17 March 2011 (UTC)

Restore definition
There are no other definitions, so the Gold Book definition can be restored. That is rather clear. The primary definition includes dipolar compounds. Some chemists do not include dipolar compounds (although no definition is given for such case, thus cannot be included into the article. The primary definition is supported by other sources, the secondary definition is not supported by other sources. The nonsense about "Related compounds" is not based on any source.--Wickey-nl (talk) 11:14, 19 March 2011 (UTC)


 * Just quote the Gold Book directly if you're going to quote it at all. Don't include your own interpretation. Definition 1 clearly has plenty of support in the lit, but just because we haven't found definition 2 clearly stated yet, doesn't mean it isn't there. We haven't looked very hard.


 * Ben (talk) 12:56, 19 March 2011 (UTC)
 * Wickey-nl, you and couple of other editors (for example, PlasmaPhysics) are trying to do the right things by relying on rules that you read, but chemists just do not use the term zwitterion in the way that you interpret the IUPAC book. Zwitterions to a chemist are almost always things like amino-acids with two separate groups.  The German article also takes this position - two functional groups that have opposite charges (ein Molekül mit zwei oder mehreren funktionellen Gruppen, von denen eine positiv und eine andere negativ geladen ist.). Wikipedia is a poor mechanism to change people's ideas, Wikipedia seeks to explain mainstream concepts.  IUPAC is a rule-making body that often deviates from mainstream thought, therefore Wikipedia editors often accept or ignore IUPAC recommendations according to our understanding of mainstream thought. Mainstream journal and textbooks never or rarely refer to dipoles as zwitterions. Informed editors can always find some way of bending a definition, but we are not here to split hairs but to present conventional interpretations.  Anyway, the consensus of the editors is against your views (including those editors that have left this page in exasperation over your ideas). Best wishes,--Smokefoot (talk) 14:14, 19 March 2011 (UTC)
 * I completely agree. Chris (talk) 15:58, 19 March 2011 (UTC)


 * If your opinion is a mainstream opinion, you can certainly find a lot of support in literature. Wikipedia as a quasi-scientific encyclopedia is without doubt filled with mainstream thoughts. It is known to be written for about 90 % by young male students and it is maintained by mainly an inbreeding of quasi-scientists and burocrates. Your opinions are true because you are "experts"; you are experts because your opinions are true.--Wickey-nl (talk) 14:23, 20 March 2011 (UTC)


 * No, Smokefoot and Chris are experts because of their qualifications and experience.
 * Ben (talk) 17:20, 20 March 2011 (UTC)

Problem with "Related Compounds"
The section as it stands is inconsistent with the first reference. The beginning of the sentence reads "Dipolar compounds are usually not classified as zwitterions. For example, amine oxides, which are often written as R3N+O−, are not zwitterions in terms of the definition,[1]" however, upon consulting the source Zwitterionic compounds, although the definition is given one finds thrimethylamine oxide, an amine oxide, as an example of a zwitterion in there. I'm not advocating for or against amine oxides being called zwitterions, which seems to be a controversial subject judging from the talk page, but there is a clear contradiction here. The section proceeds to explain where the distinction is by means of an elaborate argument but without citing any sources. As it stands the section reads somewhat like an opinion piece, trying to disprove a view that the author considers "mistaken", but failing to provide sources except a single source in which the "mistaken" view is held. I have, at least, added failed verification and citation needed tags to the first sentence and to the explanation until this problems are addressed. IgnacioPickering (talk) 04:04, 31 December 2016 (UTC)

The recent edit does not address the problem, it links to a different source which explains what dipolar compounds are, but does not rule whether they are zwitterions or not. I suggest citing a secondary source where the distinction, if there is one, is clearly stated either implicitly or explicitly. It seems to me IUPAC's goldbook implies, in source Zwitterionic compounds thet there is no disctinction or thet, if there is one it is not universally accepted. As a chemist myself I have never referred to amine oxides as zwitterions, so I sympathise, but without a source that states that they aren't and why that is so, the case can't be made that they are not. For what it's worth these are my two cents: No molecule has "unit electric charges located on atoms". If one were to plot the charge density of, for instance, alanine, and integrate it around the protonated basic nitrogen it would probably take some dubious fine tuning to get to a value of +1e. Charge density is always slightly delocalized. I probably agree that amine oxides may have a more delocalized charge density than, say, an aminoacid in its isoelectric point, but: 1) I can't be 100% sure that is indeed the case without a source, and 2) Even if that were the case this is a subtle enough point that I assume IUPAC people realize that and that's why they dumped an amine oxide with the other zwitterions in their definition. I doubt it is very useful to run an electronic structure simulation each time we have to decide if a compound is a zwitterion or just "dipolar". Regarding "canonical structures" pauling himself arguably always thought of bonds as combinations or superpositions of ionic and covalent resonance structures, so if one is strict, according to that definition a protonated amine group has, for instance, at least one canonical structure H2N+-H <-> -H2N H+. IgnacioPickering (talk) 20:53, 2 January 2017 (UTC)


 * It is a little difficult to find an authoritative source stating what something is not. It seems.  So the request at zwitterion asking for a source stating that dipoles are not zwitterions could be difficult to respond to.  Maybe others have some insights? I read a lot of scientific papers and none of them talk about what things are not.  I mean I could say that black is white and then demand that editors find a definitive article states the contrary.--Smokefoot (talk) 20:57, 2 January 2017 (UTC)


 * Well, this is a primary source, so it is perhaps not 100% satisfactory, but at least it's something http://pubs.acs.org/doi/pdf/10.1021/la00053a006, it is paywalled, but the first page already makes some sort of distinction. My point wasn't whether it is difficult or not to find an authoritative source, my point is that I don't think it's adequate to cite a source implying that it says something when it doesn't, doesn't matter if you know it to be true. I feel that can lead to dark places =P. If this source isn't clear enough perhaps the paragraph on dipolar compounds should be rewritten as to explain that dipolar compounds have separated charges in one or more resonant structures, and to not specifically make the distinction whether they are or are not zwitterions. If one or two sources like this one were found one could make the claim that "they are preferably not referred to as zwitterions" or if conflicting views are found that "usage is not totally consistent" perhaps? IgnacioPickering (talk) 21:17, 2 January 2017 (UTC)


 * For instance, IUPAC's 2004 blue book's "draft" http://old.iupac.org/reports/provisional/abstract04/BB-prs310305/CompleteDraft.pdf (links to pdf, page 580) lists "as zwitterions" clearly as a way to name amine oxides, I think at least the fact that amine oxides are permitted to be named as zwitterions by the IUPAC should be mentioned, perhaps making it clear that the usage is not common in the literature. IgnacioPickering (talk) 21:39, 2 January 2017 (UTC)


 * A quick search in J chem educ led me to http://pubs.acs.org/doi/abs/10.1021/ed036p336, where individual resonant structures with separated charges are referred to as "zwitterionic", so this "freer" usage is, at least, not unheard of in the literature, probably a little more effort will lead to something more concrete, but I think we can agree that the usage is not exactly clear cut, and trying to separate both concepts so sharply in the article is somewhat misleading. Also, I would like to point out that I'm not argueing about the difference between "dipoles and zwitterions". It's pretty clear to me that not every molecule with a nonzero dipole in a bond should be called a zwitterion, if that were the case all compounds except for strictly pure elemental forms, e.g. N2, O2, Fe(s), would be zwitterions, and that would be silly. The distinction is a subtler one, between compounds with charges sharply separated between atoms far away (e.g. aminoacids, peptides, and lots of other organic compounds), and compounds with very important resonant structures that have separated charges in atoms close to each other (e.g. amine oxides and 1,3 dipolar compounds). I want to stress that your view seems valid to me and I wouldn't have much problem accepting it myself, but that's not the question here, the question is what the term actually means, how it is used in the literature, whether the use is consistent or not, if IUPAC recommends to name them in one way or other, etc. IgnacioPickering (talk) 22:12, 2 January 2017 (UTC)

User:IgnacioPickering and User:Smokefoot, I've had a stab at reconciling the two concepts. A zwitterion is clearly dipolar. It's as dipolar as it gets. As pointed out above, not all dipoles are zwitterions (obviously). All the sources also clearly state that the resonance structures that are used to describe the charge delocalisation of dipolar molecules are formally given as zwitterions (even though these zwitterionic states don't have physical existence). Note that things like amino acids, at the right pH are demonstrably stable zwitterions with unit charges, as the IUPAC book says. I think the new wording brings the text back to a point where it doesn't go beyond the definition in the source. --Slashme (talk) 20:18, 2 November 2017 (UTC)

zwitterion
The removed section was irrelevant. The two examples cited merely showed that a zwitterion can itself have isomeric forms. The mean value pKa values cited in this section are also irrelevant as the two values from which they are derived refer to two different degrees of protonation. Petergans (talk) 12:41, 5 March 2020 (UTC)

Isoelectric point
(Lede) For many amino acids, the isoelectric point can be calculated as the mean of the two pKa values of the molecule. For a derivation of this expression see acid dissociation constant.


 * $$ \mathrm{pI} = \frac{\mathrm{p}K_\mathrm{a1} + \mathrm{p}K_\mathrm{a2}}{2} $$

The zwitterion, H3N-R-CO2, on the other hand is isomeric with the molecule H2N-R-CO2H Petergans (talk) 16:56, 5 March 2020 (UTC)

Revised version
The revised version of this article makes clear the distinction between the two types of zwitterion and restores the description of the quantitative aspect of zwitterion formation. Petergans (talk) 09:37, 18 March 2020 (UTC)
 * I agree with making these sorts of distinctions. But WP:V is policy, we can't rely on chemist-editors' WP:OR or proof-by-assertion. Make sure you do not replace, for example, an IUPAC-cited definition with anything less-well-cited (for example, no cite for the definition, uncited claim about chronology of proton transfer in amino acids (and makes an implicit claim that water is required). It's not helpful, and not a good time-investment for others to have to keep tracking that sort of editorial mistake carefully for you. DMacks (talk) 03:53, 29 March 2020 (UTC)


 * Wholesale reversion (WP:Baby and bathwater) to a previous version is an unaccepable procedure. Furthermore,
 * 1) The Gold-book definition of zwitterion is clearly defective.
 * Neutral compounds having formal unit electrical charges of opposite sign. Some chemists restrict the term to compounds with the charges on non-adjacent atoms. Sometimes referred to as inner salts, dipolar ions (a misnomer). E.g. H3N+CH2C(=O)O− ammonioacetate (glycine), (CH3)3N+–O− trimethylamine oxide.
 * Amine oxides are not zwitterions. The + and - signs in (CH3)3N+–O− refer to a specific canonical form in the valence-bond theory resonance hybrid, not real electrical charges. In zwitterions the electrical charges are real. There are occasions, of which this is one, where the Gold-book definition is defective.
 * 2) Isolectric point is irrelevant: it's a property related to the composition of a mixture of different chemical compouns in a solution. A zwitterion is one isomer of a single chemical compound.
 * 3) Dipolar compounds. The Gold-book definition is clear
 * Electrically neutral molecules carrying a positive and a negative charge in one of their major canonical descriptions.
 * This, too, derives from valence-bond theory and is irrelevant as the electrical charges in a zwitterion are real, not calculated. "Canonical descripions" are specific to VB theory; with MO theory charge density is distributed smoothly over the whole molecule; the charges in a zwitterion molecule are predominately localised.
 * The charges are shown on a zwitterion because the chemical formula H3CNCH2CO2, with 4 bonds and no charge on the N atom and an uncharged carboxylate group, would look very strange. −Petergans (talk) 11:15, 29 March 2020 (UTC)
 * You're welcome to claim whatever you want is defective, and I agree with some things looking strange. But that's all WP:OR, which is not allowed. Instead, citing WP:RS is the standard. Bottom line is the WP:BURDEN is yours (that's a wikipedia site policy, regardless of WP essays to the contrary)--you are making multiple new factual claims, some of which are easily contradicted, in addition to removing valid cites leaving uncited (though reasonably correct-looking) content. I'll start from yours, re-add the necessary cites, and then remove/tag the uncited content so you can see what work you have to do if you wish that content to remain... DMacks (talk) 11:46, 29 March 2020 (UTC)

"The value of K cannot be determined experimentally" It is impossible to verify this statement, which is based in the absence of any relevant publication. Various estimates are cited in Splittgerber and Chinander. Petergans (talk) 12:08, 1 April 2020 (UTC)
 * "Cannot" is a positive statement, and the WP:BURDEN (that's a wikipedia policy) is on you to support it with proof, since I dispute that it's definitely true. Evidence of absence ≠ absence of evidence. "It is impossible to verify this statement" pretty well sums up why it is not acceptable to write it in this article, because verifiability is one of our core policies. DMacks (talk) 03:52, 2 April 2020 (UTC)
 * The proof is that there is no publication in which the value has been determined. Therefore it is a positive statement, like "ghosts do not exist". Petergans (talk) 09:08, 2 April 2020 (UTC)
 * "Ghosts do not exist" is a positive statement that's verifiable and logically/philsophically proveable/supported by various logical/philosopgical arguments, supported by several cited WP:RS at our ghost article. "It hasn't" is not nearly the same as "it can't". Even googling [zwitterion equilibrium] and similiar phrases finds papers that propose ideas and doesn't disprove them as "impossible". DMacks (talk) 09:28, 2 April 2020 (UTC)

EDTA is not an amino acid; that's why it is not mentioned in the article amino acid. EDTA belongs to the class of molecules known as aminopolycarboxylic acids. Petergans (talk) 13:13, 2 April 2020 (UTC)
 * And xylene is not a liquid because it is not mentioned in the article liquid.--Smokefoot (talk) 16:53, 3 April 2020 (UTC)
 * The aminopolycarboxylic acid article about that class says that glycine is the parent structure (though obviously that is is mono not polycarboxylic). But it includes aspartic acid as an example, which clearly meets the definition (and our article on that chemical agrees), and that chemical I think is unarguably also an amino acid. What is your exact definition of "amino acid", that would include the usual natural and synethetic biochemical ones but exclude EDTA? I note that the Skoog ref explicitly says it behaves as an AA in this context. And it is equivalent to all the structural, chemical, and mathematical details in the AA section of this article, being a treatment of "amine + carboxylic acid ammonium + carboxylate" by eye and also per cited ref. And even in science-pub-for-lay-readers EDTA is specifically called an "amino acid" (not just having similar behavior as one). Please post your ref that it is not, as I have posted several refs that it is and behaves as one in the context here. DMacks (talk) 04:11, 3 April 2020 (UTC)
 * EDTA is not mentioned at all in the article amino acid, as clearly stated above. Therefore a link in this article to that one serves no purpose. Petergans (talk) 07:29, 3 April 2020 (UTC)

Alternate article structure

 * Maybe an underlying problem is that the section is titled "Amino acids" but its content is a mis-mosh (technical term:) of "amine/acid" (reasonably explained with math, much better than it was) and side-chain involvement (which is not covered by that math and is only relevant to some AAs). As such, we're forced into a split decision on what is actually in scope of that section. How about instead we make one section about equilibrium cases and the other about permanent (betaine) cases. Then the equilibrium-cases section can have a subsection for amine/acid (the definition of amino acid" being completely irrelevant to the math). No matter how you classify EDTA as a chemical, it's the same situation structurally, mathematically, and per cited ref as an AA, so it goes together. And another equilibrium-cases subsection for others, such as cysteine (it's an "amino acid" but the zwitterion idea is "amine/thiol" so the amine/acid math and structure-analysis is clearly different), arginine (it's an "amino acid" but the zwitterion is "guanidine/acid"), Psilocybin ("amine/phosphoric-acid"), etc.
 * That is:


 * DMacks (talk) 03:57, 6 April 2020 (UTC)
 * Structure of Anthranilic acid added. For the other examples, we need factual evidence. DFT results may be valid but a calculated structure is not verifiable. I will add a suitable phrase. Is there a citable reference for the B6 structure? If so, please add it to the text. Petergans (talk) 07:56, 6 April 2020 (UTC)
 * I think you pasted the wrong DOI for the anthranilic acid structure. But 10.1107/S0108270185004206 is even better (neutron diffraction to actually see the H rather than X-ray that only sees the heavies and relies on using "difference of C–O bond-lengths" to infer protonation sites). It should go into the Anthranilic acid article also. DMacks (talk) 08:27, 6 April 2020 (UTC)

Wrong condensed molecular formula for amino acid
I'm not really familiar with the conventions of these condensed molecular formulas, but an H from the chiral carbon sure seems to be getting dropped somewhere!

The current content is:

The equilibrium is established in two stages. In the first stage, a proton is transferred from the carboxyl group to a water molecule:



Eden hochbaum (talk) 20:22, 19 March 2023 (UTC)
 * ✅. Good catch. --Smokefoot (talk) 01:46, 20 March 2023 (UTC)