Imperial College London

Henry Rzepa

Chemistry rarely makes it to the cover of popular science magazines.
Thus when this week, the New Scientist ran the headline "*Forbidden
chemistry. Reactions they said could never happen*", I was naturally
intrigued. The examples included Woodward and Hoffmann's
"*symmetry-forbidden*" reactions, which have been the subject of several
posts here already. But in the section on nobel gas chemistry, the same
Hoffmann is reported as having been shocked to hear of a compound of
xenon and gold, both of which in their time were thought of as solidly
inert, and therefore even more unlikely to form a union.

![](http://www.ch.imperial.ac.uk/rzepa/blog/wp-content/uploads/2012/01/auxe.svg "auxe"){.aligncenter
.size-full .wp-image-6070 decoding="async"
onclick="jmolInitialize('../Jmol/');jmolSetAppletColor('green');jmolApplet([450,450],'load wp-content/uploads/2012/01/icsd_411365.mol;measure 1 2;');"}  
Science magazines are often fearful of showing molecular structures on
their pages (much like mathematical equations) and so the "shocking"
compound is not illustrated in the article; you can see the essential
feature above (the counterion is the otherwise unremarkable
Sb~2~F~11~^--^). Here, I include the 3D crystallographic coordinates
(published in
[10.1126/science.290.5489.117](http://dx.doi.org/10.1126/science.290.5489.117){target="_blank"}) which
you can explore by clicking on the above graphic or view below as a
rotatable 3D model.

Since the year 2000, when the above was reported, there have been very
few additional examples, and so it remains a rare phenomenon. I thought
it might be amusing to also give an example of the reverse phenomenon, a
reaction that chemists said *should* happen, but which they had great
difficulty in inducing, namely the formation of ***perbromate*** salts.
The reaction was [eventually
induced](http://dx.doi.org/10.1021/ja01009a040){target="_blank"} by
resorting to nuclear physics, and the radioactive transmutation of
Se^83^ to Br^83^. Once chemists had been persuaded it really could be
made, lots of more conventional ways of preparing perbromates were
discovered.

Finally, I ponder how long it might take for magazines such as New
Scientist to include interactive diagrams such as the below on the pages
of the (increasingly) electronically delivered editions? Or indeed, when
mainstream chemistry journals might start incorporating "HTML5" into
their own production processes.

 

::: {.wp_orcid_field}
[https://orcid.org/0000-0002-8635-8390](https://orcid.org/0000-0002-8635-8390){target="_blank"
rel="author"}
:::


Chemistry rarely makes it to the cover of popular science magazines. Thus when this week, the New Scientist ran the headline “
<em>
 Forbidden chemistry. Reactions they said could never happen
</em>
”, I was naturally intrigued. The examples included Woodward and Hoffmann’s “
<em>
 symmetry-forbidden
</em>
” reactions, which have been the subject of several posts here already.

Messaggi di Rogue Scholar

The “shocking” Xe-Au bond.