Posts Tagged ‘Organic chemistry’
Friday, May 22nd, 2015
As I have noted elsewhere, Gilbert N. Lewis wrote a famous paper entitled “the atom and the molecule“, the centenary of which is coming up.[1] In a short and rarely commented upon remark, he speculates about the shared electron pair structure of acetylene, R-X≡X-R (R=H, X=C). It could, he suggests, take up three forms. H-C:::C-H and two more which I show as he drew them. The first of these would now be called a bis-carbene and the second a biradical.
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References
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G.N. Lewis, "THE ATOM AND THE MOLECULE.", Journal of the American Chemical Society, vol. 38, pp. 762-785, 1916. http://dx.doi.org/10.1021/ja02261a002
Tags:Carbene, Carbenes, Chemical IT, Chemistry, Cluster chemistry, food, Functional groups, Gilbert N. Lewis, Historical, Interesting chemistry, Non-Kekulé molecule, Organic chemistry, Organic compounds
Posted in Uncategorised | 1 Comment »
Tuesday, May 12th, 2015
The Bürgi–Dunitz angle is one of those memes that most students of organic chemistry remember. It hypothesizes the geometry of attack of a nucleophile on a trigonal unsaturated (sp2) carbon in a molecule such as ketone, aldehyde, ester, and amide carbonyl. Its value obviously depends on the exact system, but is generally taken to be in the range 105-107°. A very good test of this approach is to search the crystal structure database (this was how it was originally established[1]).
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References
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H. B:urgi, J. Dunitz, J. Lehn, and G. Wipff, "Stereochemistry of reaction paths at carbonyl centres", Tetrahedron, vol. 30, pp. 1563-1572, 1974. http://dx.doi.org/10.1016/S0040-4020(01)90678-7
Tags:alkene, Bürgi–Dunitz angle, Carbonyl, Chemical IT, Chemistry, Functional groups, Group of Eight, Ketone, Organic chemistry, Organic compounds, Stall
Posted in crystal_structure_mining | 3 Comments »
Friday, April 17th, 2015
The knowledge that substituents on a benzene ring direct an electrophile engaged in a ring substitution reaction according to whether they withdraw or donate electrons is very old.[1] Introductory organic chemistry tells us that electron donating substituents promote the ortho and para positions over the meta. Here I try to recover some of this information by searching crystal structures.
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References
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H.E. Armstrong, "XXVIII.—An explanation of the laws which govern substitution in the case of benzenoid compounds", J. Chem. Soc., Trans., vol. 51, pp. 258-268, 1887. http://dx.doi.org/10.1039/CT8875100258
Tags:above search, Aromatic compounds, aromaticity, Birch reduction, Chemical IT, Chemistry, electron donating, Electrophile, Electrophilic aromatic substitution, Ether, Functional groups, little search, Organic chemistry, Physical organic chemistry, Substitution reactions
Posted in crystal_structure_mining | 1 Comment »