I reminisced about the wonderfully naive but exciting Web-period of 1993-1994. This introduced the server-log analysis to us for the first time, and hits-on-a-web-page. One of our first attempts at crowd-sourcing and analysis was to run an electronic conference in heterocyclic chemistry and to look at how the attendees visited the individual posters and presentations by analysing the server logs.
Internet Archaeology: Blasts from the past.
October 11th, 2013In 1993-1994, when the Web (synonymous in most minds now with the Internet) was still young, the pace of progress was so rapid that some wag worked out that one “web-year” was like a dog-year, worth about 7 years of normal human time. So in this respect, 1994 is now some 133 web-years ago. Long enough for an archaeological excavation.
A short non-bonding H…H interaction (continued)
October 2nd, 2013This is a continuation of the discussion started on Steve Bachrach’s blog about a molecule with a very short H…H interaction involving two Si-H groups with enforced proximity. It had been inferred from the X-ray structure[cite]10.1021/ja407398w[/cite] that the H…H distance was in the region of 1.50Å. It’s that cis-butene all over again! So is that H…H region a bond? Is it attractive or repulsive? Go read Steve’s blog first.
Publishing a procedure with a doi.
October 2nd, 2013In the two-publisher model I proposed a post or so back, I showed an example of how data can be incorporated (transcluded) into the story narrative of a scientific article, with both that story and the data each having their own independently citable reference (using a doi for the citation). Here I take it a step further, by publishing a functional procedure in a digital repository[cite]10.6084/m9.figshare.811862[/cite] and assigned its own doi:10.6084/m9.figshare.811862.
An example of an extreme gauche effect: FSSF.
September 21st, 2013The best known example of the gauche effect is 1,2-difluoroethane, which exhibits a relatively small preference of ~0.5 kcal/mol for this conformer over the anti orientation, which is also a minimum. But FSSF, which I discussed in the previous post, beats this hands down! It also, by the way, must surely be the smallest molecule (only four atoms) which could be theoretically resolved into two enantiomers (possibly at say 273K?).‡
Patterns of behaviour: serendipity in action for enantiomerisation of F-S-S-Cl
September 19th, 2013Paul Schleyer sent me an email about a pattern he had spotted, between my post on F3SSF and some work he and Michael Mauksch had done 13 years ago with the intriguing title “Demonstration of Chiral Enantiomerization in a Four-Atom Molecule“.[cite]http://doi.org/d8g2nw[/cite] Let me explain the connection, but also to follow-up further on what I discovered in that post and how a new connection evolved.
A two-publisher model for the scientific article: narrative+shared data.
September 15th, 2013I do go on rather a lot about enabling or hyper-activating[cite]10.1039/P29950000007[/cite] data. So do others[cite]10.1038/nj7461-243a[/cite]. Why is sharing data important?
The dimer of SF2: small is beautiful (and weird).
September 12th, 2013Andy Extance at the Chemistry World blog has picked up on a fascinating article[cite]10.1021/jz401578h[/cite] on the dimer of SF2. This molecule has three F atoms on one S, and only one on the other; FSSF3. But all four S-F bonds are of different length. Lindquist and Dunning claim that the minimum energy pathway to dissociation to two SF2 molecules does not involve breaking either the longest or the weakest SF bond. This was too much for me to resist investigating further!
Coarctate reactions as a third fundamental organic-mechanistic type.
September 4th, 2013According to Herges[cite]10.1021/ci00017a011[/cite],[cite]10.1039/c2cc34026g[/cite] the mechanism of single-step (concerted) reactions can be divided into three basic types; linear (e.g. substitution, elimination etc), pericyclic (e.g. Diels Alder) and a third much rarer, and hence very often overlooked type that was named coarctate. This is based on the topology of bond redistribution patterns, an explicit real example[cite]bhsn4t[/cite] illustrating:
Experimental evidence for “hidden intermediates”? Epoxidation of ethene by peracid.
August 25th, 2013The concept of a “hidden intermediate” in a reaction pathway has been promoted by Dieter Cremer[cite]10.1021/ar900013p[/cite] and much invoked on this blog. When I used this term in a recent article of ours[cite]10.1021/jo401146k[/cite], a referee tried to object, saying it was not in common use in chemistry. The term clearly has an image problem. A colleague recently sent me an article to read (thanks Chris!) about isotope effects in the epoxidation of ethene[cite]10.1021/jo981652x[/cite] and there I discovered a nice example of hidden intermediates which I share with you now.