Noting that in the coming week I am not attending the ELIXIR All Hands in Uppsala. Having lived in (and around) Uppsala for more than three years, I am disappointed and with the first stories from colleagues coming in even more. But it has been a way too busy year, I have much to finish up, and I need to take care of myself too. I am not 32 anymore. But in the past two weeks I did attend two workshops.
Some days ago, I started added boiling points to Wikidata, referenced from Basic Laboratory and Industrial Chemicals (wikidata:Q22236188), David R. Lide’s ‘a CRC quick reference handbook’ from 1993 (well, the edition I have). But Wikidata wants pressure (wikidata:P2077) info at which the boiling point (wikidata:P2102) was measured. Rightfully so. But I had not added those yet, because it slows me and can be automated with QuickStatements.
Ken Houk’s group has recently published this study of cycloaddition reactions, using a combination of classical transition state location followed by molecular dynamics trajectory calculations,[cite]10.1021/jacs.8b12674[/cite] and to which Steve Bachrach’s blog alerted me. The reaction struck me as being quite polar (with cyano groups) and so I took a look at the article to see what both the original[cite]10.1021/jo00042a039[/cite] experimental
The topic of this post originates from a recent article which is attracting much attention.[cite]10.1038/s41586-019-1059-9[/cite] The technique uses confined light to both increase the spatial resolution by around three orders of magnitude and also to amplify the signal from individual molecules to the point it can be recorded. To me, Figure 3 in this article summarises it nicely (caption: visualization of vibrational normal modes ).
There is a predilection amongst chemists for collecting records; one common theme is the length of particular bonds, either the shortest or the longest.
Five years back, I speculated about the mechanism of the epoxidation of ethene by a peracid, concluding that kinetic isotope effects provided interesting evidence that this mechanism is highly asynchronous and involves a so-called “hidden intermediate”. Here I revisit this reaction in which a small change is applied to the atoms involved. Below are two representations of the mechanism.
Recently, the 100th anniversary of the birth of the famous chemist Derek Barton was celebrated with a symposium. One of the many wonderful talks presented was by Tobias Ritter and entitled “ Late-stage fluorination for PET imaging ” and this resonated for me. The challenge is how to produce C-F bonds under mild conditions quickly so that 18 F-labelled substrates can be injected for the PET imaging.
In the previous post, I investigated the mechanism of cyclopropanation of an enal using a benzylic chloride using a quantum chemistry based procedure. Here I take a look at the NMR spectra of the resulting cyclopropane products, with an evaluation of the original stereochemical assignments.[cite]10.1021/acs.jchemed.7b00566[/cite] Three products were identified, 4a-c (aryl=2,4-dinitro) with a fourth diastereomer undetected.
Following the general recognition of carbon as being tetrahedrally tetravalent in 1869 (Paterno) and 1874 (Van’t Hoff and Le Bell), an early seminal exploitation of this to the conformation of cyclohexane was by Hermann Sachse in 1890.[cite]10.1002/cber.189002301216 [/cite] This was verified when the Braggs in 1913[cite]10.1098/rspa.1913.0084[/cite], followed by an oft-cited article by Mohr in 1918,[cite]10.1002/prac.19180980123[/cite]
