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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 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)
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)
How should the word "zwitterion" be pronounced?
83.30.188.212 15:56, 30 August 2007 (UTC)
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)
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 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)
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)
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)
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)
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)
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)
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.
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
"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)
^^^^^^^^^^^^^^^^^^^^^^^
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:
-- 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)
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)
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)
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)
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)
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.
Source | Definition | Notes |
---|---|---|
Clayden | "Ylids (or ylides) are zwitterions in which the charges are on adjacent atoms" — p. 1074. "A neutral species that contains both a positive and a negative charge is called a zwitterion." — p. 183 | |
March | doesn't seem to mention dipoles and zwitterions in the same place anywhere | |
Carey & Sundberg | talks about zwitterionic S1 excited singlet state of ethene, H2C+—C−H2, which is a 1,2-dipole | |
W. Sander, Angew. Chem. Int. Ed. Engl. (1990) 29, 344–354 | Calls carbonyl oxides, R2C=O+—O−, zwitterions. Carbonyl oxides are 1,2-dipoles ∴ definition 1 is in operation. | |
B. Braida et al, J. Am. Chem. Soc. (2010) 132, 7631–7637 | Each 1,3-dipole is described as a linear combination of three valence bond structures, two zwitterions and one diradical |
Here are a few Web of Science searches to help us out:
Ben ( talk) 14:37, 12 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)
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 Wikipedia:Lamest edit wars.
Ben ( talk) 17:30, 14 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)
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)
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)
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)
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)
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)
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)
(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.
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)
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)
"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)
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)
Bulk of the current §Amino acids, including math, discussion of differences depending on physical state, but not scoped to "proteinogenic" as the relevant definition of "amino acids". Anthranilic acid is an interesting case
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)
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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 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)
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)
How should the word "zwitterion" be pronounced?
83.30.188.212 15:56, 30 August 2007 (UTC)
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)
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 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)
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)
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)
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)
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)
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)
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.
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
"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)
^^^^^^^^^^^^^^^^^^^^^^^
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:
-- 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)
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)
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)
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)
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)
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.
Source | Definition | Notes |
---|---|---|
Clayden | "Ylids (or ylides) are zwitterions in which the charges are on adjacent atoms" — p. 1074. "A neutral species that contains both a positive and a negative charge is called a zwitterion." — p. 183 | |
March | doesn't seem to mention dipoles and zwitterions in the same place anywhere | |
Carey & Sundberg | talks about zwitterionic S1 excited singlet state of ethene, H2C+—C−H2, which is a 1,2-dipole | |
W. Sander, Angew. Chem. Int. Ed. Engl. (1990) 29, 344–354 | Calls carbonyl oxides, R2C=O+—O−, zwitterions. Carbonyl oxides are 1,2-dipoles ∴ definition 1 is in operation. | |
B. Braida et al, J. Am. Chem. Soc. (2010) 132, 7631–7637 | Each 1,3-dipole is described as a linear combination of three valence bond structures, two zwitterions and one diradical |
Here are a few Web of Science searches to help us out:
Ben ( talk) 14:37, 12 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)
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 Wikipedia:Lamest edit wars.
Ben ( talk) 17:30, 14 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)
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)
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)
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)
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)
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)
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)
(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.
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)
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)
"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)
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)
Bulk of the current §Amino acids, including math, discussion of differences depending on physical state, but not scoped to "proteinogenic" as the relevant definition of "amino acids". Anthranilic acid is an interesting case
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)