This is another of those textbook reactions, involving reaction of a carbonyl compound with a phosphonium ylid to form an alkene and a phosphine oxide. The reaction continues to be frequently used, in part because it can be highly stereospecific.
The stereochemical origins of the Wittig reaction.
August 7th, 2012The Curtius rearrangement. One step or two?
August 6th, 2012The Curtius reaction is represented in most chemistry texts and notes as following path (a) below. It is one of a general class of thermally induced rearrangement which might be described as elimination/migration (in a sense similar to this ring contraction migration/elimination), in this case implicating a nitrene intermediate if the two steps occur consecutively. Wikipedia is normally very much on the ball with this sort of thing, and a comment about the reaction mechanism there notes that current evidence prefers route (b), avoiding nitrene intermediacy (and hence formally removing this from examples of nitrene reactions).
Curly arrow pushing: another reality check.
August 5th, 2012Two years ago, I discussed how curly arrow pushing is taught, presenting four different ways of showing the arrows. One of the comments posted to that blog suggested that all of the schemes shown below were deficient in one aspect.
Cyclopentadiene: a hydrocarbon at the crossroads of …
July 29th, 2012organic 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.
QR 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[cite]10.1039/C39920000942[/cite] 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.