In an earlier post, I pondered on how the “arrow pushing” for the thermal pericyclic reactions of some annulenes (cyclic conjugated hydrocarbons) could be represented in terms of either two separate electrocyclic reactions or of one cycloaddition reaction. Each reaction is governed by selection rules which can be stated in terms of the anticipated aromaticity of the pericyclic transition state as belonging to a 4n or a 4n+2 class. This in turn determines whether the topology of the transition state belongs to a class of aromatic species known as either Hückel or Möbius. Here I play with the observation that by adding or removing two electrons from the molecule, the two classes 4n and 4n+2 can be swapped. What happens to the aromaticities of the transition states if that is done?
Trimerous pericyclic reactions: what is the effect of changing the electron count by two?
November 2nd, 2020Room-temperature superconductivity in a carbonaceous sulfur hydride!
October 17th, 2020The title of this post indicates the exciting prospect that a method of producing a room temperature superconductor has finally been achived[cite]10.1038/s41586-020-2801-z[/cite]. This is only possible at enormous pressures however; >267 gigaPascals (GPa) or 2,635,023 atmospheres.
Trimerous pericyclic reactions.
October 8th, 2020I 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.[cite]10.1021/ed084p1535[/cite] 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!
Blasts from the past: a snapshot of online content in chemistry, ~1994-1998.
September 28th, 2020With 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.
The Willgerodt-Kindler reaction. Completing the Box set.
September 7th, 2020These 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.
High-performance polythioesters with high chemical recyclability.
September 2nd, 2020Here I investigate a recent report[cite]10.1126/sciadv.abc0495[/cite] 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.
Exploiting the power of persistent identifiers (PIDs) for locating all kinds of research object.
August 29th, 2020The 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);
The Willgerodt-Kindler Reaction: mechanistic reality check 3. A peek under the hood for transition state location.
August 27th, 2020The 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.
The Willgerodt-Kindler Reaction: mechanistic reality check 2.
August 14th, 2020Continuing 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!).[cite]10.1002/jhet.5570260518[/cite] Here the key intermediate proposed is a thiirenium cation (labelled 8 in the article) and labelled Int3 below.
Question for the day – Einstein, special relativity and atomic weights.
July 25th, 2020Sometimes 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.