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Henry Rzepa's Blog

Henry Rzepa's Blog
Chemistry with a twist
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As I have noted elsewhere, Gilbert N. Lewis wrote a famous paper entitled “ the atom and the molecule ”, the centenary of which is coming up.[cite]10.1021/ja02261a002[/cite] In a short and rarely commented upon remark, he speculates about the shared electron pair structure of acetylene,  R-X≡X-R (R=H, X=C). It could, he suggests, take up three forms. H-C:::C-H and two more which I show as he drew them.

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A lunchtime conversation with a colleague had us both bemoaning the distorting influence on chemistry of bibliometrics, h-indices and journal impact factors, all very much a modern phenomenon of scientific publishing. Young academics on a promotion fast-track for example are apparently advised not to publish in a well-known journal devoted to organic chemistry because of its apparently “low” impact factor.

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Blogging in chemistry remains something of a niche activity, albeit with a variety of different styles. The most common is commentary or opinion on the scientific literature or conferencing, serving to highlight what their author considers interesting or important developments. There are even metajournals that aggregate such commentaries. The question therefore occasionally arises;

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Allotropes are differing structural forms of the elements. The best known example is that of carbon, which comes as diamond and graphite, along with the relatively recently discovered fullerenes and now graphenes. Here I ponder whether any of the halogens can have allotropes. Firstly, I am not aware of much discussion on the topic.

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Egon has reminded us that adoption of ORCID (Open researcher and collaborator ID) is gaining apace. It is a mechanism to disambiguate (a Wikipedia term!) contributions in the researcher community and to also remove much of the anonymity (where that is undesirable) that often lurks in social media sites.

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The knowledge that substituents on a benzene ring direct an electrophile engaged in a ring substitution reaction according to whether they withdraw or donate electrons is very old.[cite]10.1039/CT8875100258[/cite] Introductory organic chemistry tells us that electron donating substituents promote the ortho and para positions over the meta . Here I try to recover some of this information by searching crystal structures.

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Sodium borohydride is the tamer cousin of lithium aluminium hydride (LAH). It is used in aqueous solution to e.g. reduce aldehydes and ketones, but it leaves acids, amides and esters alone. Here I start an exploration of why it is such a different reducing agent. Initially, I am using Li, not Na (X=Li), to enable a more or less equal comparison with LAH, with water molecules to solvate rather than ether (n=2,3,5) and R set to Me.