Talk:Zwitterion

message: 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)
thread_title:  Definition concern 

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

message: 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)
replies: text: 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)
replies: text: 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)
thread_title:  Zwitterion definition 

message: 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)
replies: text: 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)

text: 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)

text: 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)

text: 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)
thread_title:  Problem with "Related Compounds" 

message: 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)
thread_title:  zwitterion 

message: (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)
thread_title: Isoelectric point

message: ::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)
replies: text: 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)
replies: text: I think you pasted the wrong DOI for the anthranilic acid structure. But doi: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)
thread_title:  Alternate article structure 

message: 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:
: H2N(R)CO2H + H2O <=> H2N(R)CO2- + H3O+
Eden hochbaum (talk) 20:22, 19 March 2023 (UTC)
replies: text: .  Good catch. --Smokefoot (talk) 01:46, 20 March 2023 (UTC)
thread_title:  Wrong condensed molecular formula for amino acid