The element silicon best represents the digital era of the mid 20th century to the present; without its crystalline form, there would be no computers (or this blog). Although it was first prepared in pure amorphous (powder) form around 1823[1] by Berzelius, it was not until 1854 that Henri Sainte-Claire Deville made it in crystalline form, using metallic aluminium to isolate it. He described it [1] as having a “metallic luster”.
The world ash tree of the computer hardware industry… crystalline silicon from 1854.
October 31st, 2013Six vs ten aromatic electrons?
October 20th, 2013Homoaromaticity is a special case of aromaticity in which π-conjugation is interrupted by a single sp3 hybridized carbon atom (it is sometimes referred to as a suspended π-bond with no underlying σ-foundation). But consider the carbene shown below. This example comes from a recently published article[1] which was highlighted on Steve Bachrach’s blog. Here aromaticity has resulted from a slightly different phenomenon, whereby a 4π-electron planar (and hence nominally anti-aromatic) molecule is elevated to aromatic peerage by promoting the two carbene σ-electrons to have π-status.
References
- B. Chen, A.Y. Rogachev, D.A. Hrovat, R. Hoffmann, and W.T. Borden, "How to Make the σ<sup>0</sup>π<sup>2</sup> Singlet the Ground State of Carbenes", Journal of the American Chemical Society, vol. 135, pp. 13954-13964, 2013. https://doi.org/10.1021/ja407116e
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[1] 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.
References
- J. Zong, J.T. Mague, and R.A. Pascal, "Exceptional Steric Congestion in an <i>in</i>,<i>in</i>-Bis(hydrosilane)", Journal of the American Chemical Society, vol. 135, pp. 13235-13237, 2013. https://doi.org/10.1021/ja407398w
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[1] and assigned its own doi:10.6084/m9.figshare.811862.
References
- H.S. Rzepa, "Script for creating an NCI surface as a JVXL compressed file from a (Gaussian) cube of total electron density", 2013. https://doi.org/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“.[1] Let me explain the connection, but also to follow-up further on what I discovered in that post and how a new connection evolved.
References
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[1] data. So do others[2]. Why is sharing data important?
References
- O. Casher, G.K. Chandramohan, M.J. Hargreaves, C. Leach, P. Murray-Rust, H.S. Rzepa, R. Sayle, and B.J. Whitaker, "Hyperactive molecules and the World-Wide-Web information system", Journal of the Chemical Society, Perkin Transactions 2, pp. 7, 1995. https://doi.org/10.1039/p29950000007
- R. Van Noorden, "Data-sharing: Everything on display", Nature, vol. 500, pp. 243-245, 2013. https://doi.org/10.1038/nj7461-243a