Room-temperature superconductivity in a carbonaceous sulfur hydride!

October 17th, 2020

The title of this post indicates the exciting prospect that a method of producing a room temperature superconductor has finally been achived[1]. This is only possible at enormous pressures however; >267 gigaPascals (GPa) or 2,635,023 atmospheres.

Read the rest of this entry »

References

  1. E. Snider, N. Dasenbrock-Gammon, R. McBride, M. Debessai, H. Vindana, K. Vencatasamy, K.V. Lawler, A. Salamat, and R.P. Dias, "Room-temperature superconductivity in a carbonaceous sulfur hydride", Nature, vol. 586, pp. 373-377, 2020. http://dx.doi.org/10.1038/s41586-020-2801-z

Trimerous pericyclic reactions.

October 8th, 2020

I occasionally spot an old blog that emerges, if only briefly, as “trending”. In this instance, only the second blog I ever wrote here, way back in 2009 as a follow up to this article.[1] With something of that age, its always worth revisiting to see if any aspect needs updating or expanding, given the uptick in interest. It related to the observation that there can be more than one way of expressing the “curly arrows” for some pericyclic reactions. These alternatives may each represent different types of such reactions, hence leading to a conundrum for students of how to label the mechanism. I had noted in that blog that I intended to revisit the topic and so a mere eleven years later here it is!

Read the rest of this entry »

References

  1. H.S. Rzepa, "The Aromaticity of Pericyclic Reaction Transition States", Journal of Chemical Education, vol. 84, pp. 1535, 2007. http://dx.doi.org/10.1021/ed084p1535

Blasts from the past: a snapshot of online content in chemistry, ~1994-1998.

September 28th, 2020

With universities around the world having to very rapidly transition to blended learning (a mixture of virtual and face-2-face experiences) with a very large component based on online materials, I thought it might be interesting to try to give one snapshot of when the online experience started to happen in chemistry.

Read the rest of this entry »

The Willgerodt-Kindler reaction. Completing the Box set.

September 7th, 2020

These four posts (the box set) set out to try to define the energetics for a reasonable reaction path for the Willgerodt-Kindler reaction. The rate of this reaction corresponds approximately to a free energy barrier of ~30 kcal/mol. Any pathway found to be >10 kcal/mol at its highest point above this barrier was deemed less probable. The first three efforts at defining such pathways all gave such a result. Here I try a fourth pathway in search of the hitherto elusive appropriately low energy barrier.

Read the rest of this entry »

High-performance polythioesters with high chemical recyclability.

September 2nd, 2020

Here I investigate a recent report[1] of a new generation of polyesters with the intrinsic properties of high crystallinity and chemical recyclability. The latter point is key, since many current plastics cannot be easily recycled to a form which can be used to regenerate the original polymer with high yield. Here I show some aspects of this fascinating new type of polymer.

Read the rest of this entry »

References

  1. C. Shi, M.L. McGraw, Z. Li, L. Cavallo, L. Falivene, and E.Y. Chen, "High-performance pan-tactic polythioesters with intrinsic crystallinity and chemical recyclability", Science Advances, vol. 6, pp. eabc0495, 2020. http://dx.doi.org/10.1126/sciadv.abc0495

Exploiting the power of persistent identifiers (PIDs) for locating all kinds of research object.

August 29th, 2020

The folks at DataCite have announced a new research object discovery service which aims to give users a “comprehensive overview of connections between entities in the research landscape”. The portal https://commons.datacite.org acts as the entry point for three basic types of persistent identifiers (PIDs);

Read the rest of this entry »

The Willgerodt-Kindler Reaction: mechanistic reality check 3. A peek under the hood for transition state location.

August 27th, 2020

The two previous surveys of the potential energy surface for this, it has to be said, rather obscure reaction led to energy barriers that were rather to high to be entirely convincing. So here is a third possibility.

Read the rest of this entry »

The Willgerodt-Kindler Reaction: mechanistic reality check 2.

August 14th, 2020

Continuing an exploration of the mechanism of this reaction, an alternative new mechanism was suggested in 1989 (having been first submitted to the journal ten years earlier!).[1] Here the key intermediate proposed is a thiirenium cation (labelled 8 in the article) and labelled Int3 below.

Read the rest of this entry »

References

  1. M. Carmack, "The willgerodt-kindler reactions. 7. The mechanisms", Journal of Heterocyclic Chemistry, vol. 26, pp. 1319-1323, 1989. http://dx.doi.org/10.1002/jhet.5570260518

Question for the day – Einstein, special relativity and atomic weights.

July 25th, 2020

Sometimes a (scientific) thought just pops into one’s mind. Most are probably best not shared with anyone, but since its the summer silly season, I thought I might with this one.

Read the rest of this entry »

The Willgerodt-Kindler Reaction: mechanistic reality check 1.

July 21st, 2020

The Willgerodt reaction[1], discovered in 1887 and shown below, represents a transformation with a once famously obscure mechanism. A major step in the elucidation of that mechanism came[2] using the then new technique of 14C radio-labelling, shortly after the atom bomb projects during WWII made 14CO2 readily available to researchers. Here I am going to start the process of applying the far more recent technique of quantitative quantum mechanical modelling to see if some of the proposed mechanisms stand up to its scrutiny.

Read the rest of this entry »

References

  1. C. Willgerodt, "Ueber die Einwirkung von gelbem Schwefelammonium auf Ketone und Chinone", Berichte der deutschen chemischen Gesellschaft, vol. 20, pp. 2467-2470, 1887. http://dx.doi.org/10.1002/cber.18870200278
  2. W.G. Dauben, J.C. Reid, P.E. Yankwich, and M. Calvin, "The Mechanism of the Willgerodt Reaction1", Journal of the American Chemical Society, vol. 72, pp. 121-124, 1950. http://dx.doi.org/10.1021/ja01157a034