I was first taught curly arrow pushing in 1968, and have myself taught it to many a generation of student since. But the other day, I learnt something new. Nick Greeves was kind enough to send me this link‡to the origin of curly arrow pushing in organic chemistry, where the following diagram is shown and Alan Dronsfield sent me two articles he co-wrote on the topic (T. M. Brown, A. T. Dronsfield and P. J. T Morris, Education in Chemistry, 2001, 38, 102-104, 107 and 2003, 40, 129-134);† thanks to both of them.
The first ever curly arrows.
July 20th, 2012Dynamic effects in nucleophilic substitution at trigonal carbon (with Na+).
July 19th, 2012In the preceding post, I described a fascinating experiment and calculation by Bogle and Singleton, in which the trajectory distribution of molecules emerging from a single transition state was used to rationalise the formation of two isomeric products 2 and 3. In the present post, I explore possible consequences of including a sodium cation (X=Na+ below) in the computational model.
Dynamic effects in nucleophilic substitution at trigonal carbon.
July 16th, 2012Singleton and co-workers have produced some wonderful work showing how dynamic effects and not just transition states can control the outcome of reactions. Steve Bachrach’s blog contains many examples, including this recent one.
More joining up of pieces. Stereocontrol in the ring opening of cyclopropenes.
July 12th, 2012Years ago, I was travelling from Cambridge to London on a train. I found myself sitting next to a chemist, and (as chemists do), he scribbled the following on a piece of paper. When I got to work the next day Vera (my student) was unleashed on the problem, and our thoughts were published[cite]10.1039/C39920001323[/cite]. That was then.
Joining up the pieces. Peroxidation of ethyne.
July 9th, 2012Sometimes, connections between different areas of chemistry just pop out (without the help of semantic web tools, this is called serendipity). So here, I will try to join up some threads which emerge from previous posts.
Connections in chemistry. Anti-malaria drug ↔ organocatalysis.
July 5th, 2012Back in 1994, we published the crystal structure of the molecule below (X=H), a putative anti-malarial drug called halofantrine. Little did we realise that a whole area of organo catalysis based on a thiourea catalyst with a similar motif would emerge a little later. Here is how the two are connected.
The direct approach is not always the best: ethene + dichlorocarbene
June 12th, 2012The reaction between a carbene and an alkene to form a cyclopropane is about as simple a reaction as one can get. But I discussed before how simple little molecules (cyclopropenyl anion) can hold surprises. So consider this reaction:
Transition state models for Baldwin dig(onal) ring closures.
June 10th, 2012This is a continuation of the previous post exploring the transition state geometries of various types of ring closure as predicted by Baldwin’s rules. I had dealt with bond formation to a trigonal (sp2) carbon; now I add a digonal (sp) example (see an interesting literature variation).
Streptomycin: a case study in the progress of science.
May 28th, 2012Streptomycin is an antibiotic active against tuberculosis, and its discovery has become something of a cause célèbre. It was first isolated on October 19, 1943 by a graduate student Albert Schatz in the laboratory of Selman Waksman at Rutgers University. I want to concentrate in this post on its molecular structure. Its initial isolation was followed by an extraordinarily concentrated period of about three years devoted to identifying that structure, culminating in a review of this chemistry in 1948 by Lemieux and Wolfram.[cite]10.1016/S0096-5332(08)60034-X[/cite] This review presents the structure as shown below (left). The modern rendering on the right is based on a crystal structure done in 1978.[cite]10.1098/rspa.1978.0047[/cite]‡