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.[cite]10.1021/ja02261a002[/cite] 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.
Posts Tagged ‘Organic chemistry’
R-X≡X-R: G. N. Lewis’ 100 year old idea.
Friday, May 22nd, 2015The Bürgi–Dunitz angle revisited: a mystery?
Tuesday, May 12th, 2015The 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[cite]10.1016/S0040-4020(01)90678-7[/cite]).
A new way of exploring the directing influence of (electron donating) substituents on benzene.
Friday, April 17th, 2015The 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.[cite]10.1039/CT8875100258[/cite] 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.