I have just noticed unexpected links between two old posts, one about benzene, one about diphenyl magnesium and a link to August Kekulé. ^† Click for 3D The post about benzene dealt with the apparently simple issue of why all the C-C bonds are of equal length. The answer, in brief is purely because of the σ-electrons. If the π-electrons had their way, benzene would have three short and three long C-C bonds.

The journal of chemical education can be a fertile source of ideas for undergraduate student experiments. Take this procedure for asymmetric epoxidation of an alkene.[cite]10.1021/ed077p271[/cite] When I first spotted it, I thought not only would it be interesting to do in the lab, but could be extended by incorporating some modern computational aspects as well.

Around 100 tons of the potent antimalarial artemisinin is produced annually; a remarkable quantity given its very unusual and fragile looking molecular structure (below). When I looked at this, I was immediately struck by a thought: surely this is a classic molecule for analyzing stereoelectronic effects (anomeric and gauche). Here this aspect is explored.

Science is rarely about a totally new observation or rationalisation, it is much more about making connections between known facts, and perhaps using these connections to extrapolate to new areas (building on the shoulders of giants, etc). So here I chart one example of such connectivity over a period of six years.

In the previous post, I showed how modelling of unbranched alkenes depended on dispersion forces. When these are included, a bent (single-hairpin) form of C ₅₈ H ₁₁₈ becomes lower in free energy than the fully extended linear form. Here I try to optimise these dispersion forces by adding further folds to see what happens.

By about C17H36, the geometry of “cold-isolated” unbranched saturated alkenes is supposed not to contain any fully anti-periplanar conformations.

OK, you have to be British to understand the pun in the title, a famous comedy skit about four candles. Back to science, and my mention of some crystal data now having a DOI in the previous post. I thought it might be fun to replicate the contents of one of my ACS slides here. Firstly, a DOI is one implementation of a more generic (and quite old) concept known as a Handle. This is one form of a persistent digital identifier.

I have mentioned the Amsterdam manifesto before on these pages. It is worth repeating the eight simple principles: Data should be considered citable products of research. Such data should be held in persistent public repositories. If a publication is based on data not included with the article, those data should be cited in the publication.

A short post this, to remind that today is officially the 25th birthday of the World-Wide-Web, in March 1989. It took five years for a conference around the theme to be organised and below is a photo from that event. (C) CERN Photo From my perspective and perhaps from the 200 or so others present at that closing session, I went back home and told my young children that the world had changed that week. So it has.

My previous post related to the aromatic electrophilic substitution of benzene using as electrophile phenyl diazonium chloride. Another prototypical reaction, and again one where benzene is too inactive for the reaction to occur easily, is the catalyst-free bromination of benzene to give bromobenzene and HBr.

The diazo-coupling reaction dates back to the 1850s (and a close association with Imperial College via the first professor of chemistry there, August von Hofmann) and its mechanism was much studied in the heyday of physical organic chemistry.[cite]10.1021/ja00830a009[/cite] Nick Greeves, purveyor of the excellent ChemTube3D site, contacted me about the transition state (I have commented previously on this aspect of aromatic