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Structure
edit( copied from usertalk:petergans)
Hi Peter, I saw that you commented out my image at Triglycine sulfate. Depicting chemical structures that contain both acidic and basic groups always presents a bit of difficulty. In most cases, it is standard practice to show such compounds in their neutral form because the protonation states of various groups can depend on conditions (solid state, in solution, etc). I don't mind if you would like to replace the image with something else, but in the absence of an alternate, I think File:Triglycine sulfate.svg is perfectly reasonable. It is similar to what is shown at PubChem, ChemSpider, and other chemical databases. Let me know what you think. -- Ed (Edgar181) 13:28, 6 May 2011 (UTC)
- My objection to the structure is that it shows sulphuric acid molecules of crystallization. This cannot be right for various reasons. I'll have to go to the library on Sunday to get details of the XL structure. Until then, please leave the structure commented out. Petergans (talk) 20:29, 6 May 2011 (UTC)
The crystal structure is not a full structure and has no details of molecular conformations. Maybe User:Materialscientist can get more details from his database. Petergans (talk) 08:06, 11 May 2011 (UTC) I found a full structure at
Choudhury, Rajul Ranjan (2008). "Single crystal neutron diffraction study of triglycine sulphate revisited". Pramana. 71 (5): 911–915. doi:10.1007/s12043-008-0199-5. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
It shows three types of "glycine" and sulfate anions. Of course if sulfate ions are present there must be protonation of glycine. Another visit to the library is needed! Petergans (talk) 08:36, 11 May 2011 (UTC)
(copied)
- Difficulties such as this are the reason that organic chemists like "idealized" representations. All the important connectivity information is conveyed simply, without having to worry about where exactly all those pesky hydrogen atoms actually reside. :) In any case, I appreciate the effort that you are putting into finding a more precise representation. Please let me know if there is anything I might do to help - I may have access at my institution's library to materials not available elsewhere. -- Ed (Edgar181) 21:00, 11 May 2011 (UTC)
I can accept the formula G3•H2SO4 as representing the stoichiometry (G=glycine). The structure, however is a different matter. Let me add a little context. TGS has been used as an infrared detector. I was surprised to find no article on TGS, so I created a stub. The point is, TGS is principally of interest in the solid state because of the pyroelectric property of its crystals. This being so, maybe a molecular structure is irrelevant? I will be able to read the n-diffraction paper when I go to the library and I'll modify the article to reflect the crystal structure. We can then see more clearly what to put in the chembox.
One other point. It's not just a matter of locating the hydrogen atoms. Glycine is a weak base (pKa 9.6) and sulfuric acid is a strong acid. Therefore the two cannot co-exist because there will be an acid-base reaction leading to protonated glycine and sulfate ions. The really interesting point is why there is a 3rd. glycine in the structure. Diglycine sulfate is known and has the formula (GH )2(SO4)2-. Petergans (talk) 10:23, 12 May 2011 (UTC)
- user:Materialscientist has added a crystal structure. I won't elaborate on the H-bonding from the n-diff. paper. Petergans (talk) 14:02, 15 May 2011 (UTC)