organic chemistry. It does not look like much, but this small little molecule brought us ferrocene, fluxional NMR, aromatic anions and valley-ridge inflexion points. You might not have heard of this last one, but in fact I mentioned the phenomenon in my post on nitrosobenzene. As for being at a crossroads, more like a Y-junction. Let me explain why.
Cyclopentadiene: a hydrocarbon at the crossroads of …
July 29th, 2012QR codes and InChI strings.
July 22nd, 2012A month or so ago at a workshop I was attending, a speaker included in his introductory slide a QR (Quick Response) Code. It is a feature of most digital eco-systems that there is probably already “an app for it”. So I thought I would jump on the band wagon by coding an InChI string. Here it is below:
Digital repositories. An update.
July 21st, 2012I blogged about this two years ago and thought a brief update might be in order now. To support the discussions here, I often perform calculations, and most of these are then deposited into a DSpace digital repository, along with metadata. Anyone wishing to have the full details of any calculation can retrieve these from the repository. Now in 2012, such repositories are more important than ever.
The first ever curly arrows. And now for something completely different.
July 21st, 2012The discussion appended to the post on curly arrows is continued here. Recollect the curly arrow diagram (in modern style) derived from Robinson’s original suggestion:
The first curly arrows…lead to this?
July 20th, 2012Little did I imagine, when I discovered the original example of using curly arrows to express mechanism, that the molecule described there might be rather too anarchic to use in my introductory tutorials on organic chemistry. Why? It simply breaks the (it has to be said to some extent informal) rules! Consider the dimerisation of nitrosomethane (in fact a well-known equilibrium).
Origins of the Regioselectivity of Cyclopropylcarbinyl Ring Opening Reactions.
July 20th, 2012Twenty years are acknowledged to be a long time in Internet/Web terms. In the early days (in 1994), it was a taken that the passage of 1 Web day in the Internet time-warp was ~≡ 7 for the rest of the world (the same factor as applied to the lives of canines). This temporal warping can also be said to apply to computational chemistry. I previously revisited some computational work done in 1992, and here I rediscover another investigation from that year[1] and that era. The aim in this post is to compare not only how the presentation of the results has changed, but how the computational models have as well.
References
- R.A. Batey, P. Grice, J.D. Harling, W.B. Motherwell, and H.S. Rzepa, "Origins of the regioselectivity of cyclopropylcarbinyl ring opening reactions in bicyclo [n.1.0] systems", Journal of the Chemical Society, Chemical Communications, pp. 942, 1992. https://doi.org/10.1039/c39920000942
The first ever curly arrows.
July 20th, 2012I 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.
Dynamic 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.