I have several times used arrow pushing on these blogs. But since the rules for this convention appear to be largely informal, and there appears to be no definitive statement of them, I thought I would try to produce this for our students. This effort is here shared on my blog. It is what I refer to as the standard version; an advanced version is in preparation. Such formality might come as a surprise to some; arrow-pushing is often regarded as far too approximate to succumb to any definition, although it is of course often examined.
Archive for the ‘General’ Category
With metrics in science publishing controversial to say the least, I pondered whether to write about the impact/influence a science-based blog might have (never mind whether it constitutes any measure of esteem). These are all terms that feature large when an (academic) organisation undertakes a survey of its researchers’ effectiveness.‡ WordPress (the organisation that provides the software used for this blog) recently enhanced the stats it offers for its users, and one of these caught my eye.
The Baldwin rules for ring closure follow the earlier ones by Bürgi and Dunitz in stating the preferred angles of nucleophilic (and electrophilic) attack in bond forming reactions, and are as famous for the interest in their exceptions as for their adherence. Both sets of rules fundamentally explore the geometry of the transition states involved in the reaction, as reflected in the activation free energies. Previous posts exploring the transition states for well-known reactions have revealed that the 4th dimension (the timing of the bond formations/breakings) can often spring surprises. So this post will explore a typical Baldwin ring formation in the same way.
Many reaction mechanisms involve a combination of bond formation/cleavage between two non-hydrogen atoms and those involving reorganisation of proximate hydrogens. The Baeyer-Villiger discussed previously illustrated a complex dance between the two types. Here I take a look at another such mechanism, the methylation of a carboxylic acid by diazomethane.
I thought I would launch the 2012 edition of this blog by writing about shared space. If you have not come across it before, it is (to quote Wikipedia), “an urban design concept aimed at integrated use of public spaces.” The BBC here in the UK ran a feature on it recently, and prominent in examples of shared space in the UK was Exhibition Road. I note this here on the blog since it is about 100m from my office.
Fascination with nano-objects, molecules which resemble every day devices, is increasing. Thus the world’s smallest car has just been built. The mechanics of such a device can often be understood in terms of chemical concepts taught to most students. So I thought I would have a go at this one!
An attosecond is 10-18s. The chemistry that takes place on this timescale is called electron dynamics. For example, it is the time taken for an electron to traverse the 1s orbit in a hydrogen atom. And chemists are starting to manipulate electrons (and hence chemistry) on this timescale; for example a recent article (DOI: 10.1021/ja206193t) describes how to control the electrons in benzene using attosecond laser pulses.