For those of us who were around in 1985, an important chemical IT innovation occurred. We could acquire a computer which could be used to draw chemical structures in one application, and via a mysterious and mostly invisible entity called the clipboard, paste it into a word processor (it was called a Macintosh). Perchance even print the result on a laserprinter. Most students of the present age have no idea what we used to do before this innovation! Perhaps not in 1985, but at some stage shortly thereafter, and in effect without most people noticing, the return journey also started working, the so-called round trip. It seemed natural that a chemical structure diagram subjected to this treatment could still be chemically edited, and that it could make the round trip repeatedly. Little did we realise how fragile this round trip might be. Years later, the computer and its clipboard, the chemistry software, and the word processor had all moved on many generations (it is important to flag that three different vendors were involved, all using proprietary formats to weave their magic). And (on a Mac at least) the round-tripping no longer worked. Upon its return to (Chemdraw in this instance), it had been rendered inert, un-editable, and devoid of semantic meaning unless a human intervened. By the way, this process of data-loss is easily demonstrated even on this blog. The chemical diagrams you see here are similarly devoid of data, being merely bit-mapped JPG images. Which is why, on many of these posts, I put in the caption Click for 3D, which gives you access to the chemical data proper (in CML or other formats). And I throw in a digital repository identifier for good measure should you want a full dataset.
Archive for November, 2010
Data-round-tripping: moving chemical data around.
Saturday, November 20th, 2010Gravitational fields and asymmetric synthesis
Saturday, November 20th, 2010Our understanding of science mostly advances in small incremental and nuanced steps (which can nevertheless be controversial) but sometimes the steps can be much larger jumps into the unknown, and hence potentially more controversial as well. More accurately, it might be e.g. relatively unexplored territory for say a chemist, but more familiar stomping ground for say a physicist. Take the area of asymmetric synthesis, which synthetic chemists would like to feel they understand. But combine this with gravity, which is outside of their normal comfort zone, albeit one we presume is understood by physicists. Around 1980, one chemist took such a large jump by combining the two, in an article spectacularly entitled Asymmetric synthesis in a confined vortex; Gravitational fields and asymmetric synthesis[1]. The experiment was actually quite simple. Isophorone (a molecule with a plane of symmetry and hence achiral) was treated with hydrogen peroxide and the optical rotation measured.
References
- R.C. Dougherty, "Chemical geometrodynamics: gravitational fields can influence the course of prochiral chemical reactions", Journal of the American Chemical Society, vol. 102, pp. 380-381, 1980. https://doi.org/10.1021/ja00521a067
Can a cyclobutadiene and carbon dioxide co-exist in a calixarene cavity?
Friday, November 19th, 2010On 8th August this year, I posted on a fascinating article that had just appeared in Science[1] in which the crystal structure was reported of two small molecules, 1,3-dimethyl cyclobutadiene and carbon dioxide, entrapped together inside a calixarene cavity. Other journals (e.g. Nature Chemistry[2] ran the article as a research highlight (where the purpose is not a critical analysis but more of an alerting service). A colleague, David Scheschkewitz, pointed me to the article. We both independently analyzed different aspects, and first David, and then I then submitted separate articles for publication describing what we had found. Science today published both David’s thoughts[3] and also those of another independent group, Igor Alabugin and colleagues[4]. The original authors have in turn responded [5]. My own article on the topic will appear very shortly[6]. You can see quite a hornet’s nest has been stirred up!
References
- Y. Legrand, A. van der Lee, and M. Barboiu, "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix", Science, vol. 329, pp. 299-302, 2010. https://doi.org/10.1126/science.1188002
- A. Pichon, "Structure of a strained ring", Nature Chemistry, 2010. https://doi.org/10.1038/nchem.823
- D. Scheschkewitz, "Comment on “Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix”", Science, vol. 330, pp. 1047-1047, 2010. https://doi.org/10.1126/science.1195752
- I.V. Alabugin, B. Gold, M. Shatruk, and K. Kovnir, "Comment on “Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix”", Science, vol. 330, pp. 1047-1047, 2010. https://doi.org/10.1126/science.1196188
- Y. Legrand, A. van der Lee, and M. Barboiu, "Response to Comments on “Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix”", Science, vol. 330, pp. 1047-1047, 2010. https://doi.org/10.1126/science.1195846
- H.S. Rzepa, "Can 1,3-dimethylcyclobutadiene and carbon dioxide co-exist inside a supramolecular cavity?", Chem. Commun., vol. 47, pp. 1851-1853, 2011. https://doi.org/10.1039/c0cc04023a
A historical detective story: 120 year old crystals
Wednesday, November 17th, 2010In 1890, chemists had to work hard to find out what the structures of their molecules were, given they had no access to the plethora of modern techniques we are used to in 2010. For example, how could they be sure what the structure of naphthalene was? Well, two such chemists, William Henry Armstrong (1847-1937) and his student William Palmer Wynne (1861-1950; I might note that despite working with toxic chemicals for years, both made it to the ripe old age of ~90!) set out on an epic 11-year journey to synthesize all possible mono, di, tri and tetra-substituted naphthalenes. Tabulating how many isomers they could make (we will call them AW here) would establish beyond doubt the basic connectivity of the naphthalene ring system. This was in fact very important, since many industrial dyes were based on this ring system, and patents depended on getting it correct! Amazingly, their collection of naphthalenes survives to this day. With the passage of 120 years, we can go back and check their assignments. The catalogued collection (located at Imperial College) comprises 263 specimens. Here the focus is on just one, specimen number number 22, which bears an original label of trichloronaphthalene [2:3:1] and for which was claimed a melting point of 109.5°C. What caught our attention is that a search for this compound in modern databases (Reaxys if you are interested, what used to be called Beilstein) reveals the compound to have a melting point of ~84°C. So, are alarm bells ringing? Did AW make a big error? Were many of the patented dyes not what they seemed?