In the previous post, I found intriguing the mechanism by which methane (CH 4 ) inverts by transposing two of its hydrogens. Here I take a look at silane, SiH 4 . It appears it is a three-stage process! Firstly, silane eliminates molecular hydrogen to form a molecular complex between H 2 and SiH 2 (DOI: 10.14469/hpc/2290). The barrier (~60 kcal/mol) is very much lower than with methane.
This is a spin-off from the table I constructed here for further chemical examples of the classical/non-classical norbornyl cation conundrum. One possible entry would include the transition state for inversion of methane via a square planar geometry as compared with e.g. NiH 4 for which the square planar motif is its minimum.
This is another of those posts that has morphed from an earlier one noting the death of the great chemist George Olah.
George Olah passed away on March 8th. He was part of the generation of scientists in the post-war 1950s who had access to chemical instrumentation that truly revolutionised chemistry.
A few years back, I did a post about the Pirkle reagent[cite]10.1039/c39910000765[/cite] and the unusual π-facial hydrogen bonding structure[cite]10.1039/P29940000703[/cite] it exhibits. For the Pirkle reagent, this bonding manifests as a close contact between the acidic OH hydrogen and the edge of a phenyl ring; the hydrogen bond is off-centre from the middle of the aryl ring.
Living in London, travelling using public transport is often the best way to get around. Before setting out on a journey one checks the status of the network. Doing so today I came across this page: our open data from Transport for London. I learnt that by making TFL travel data openly available, some 11,000 developers (sic!) have registered for access, out of which some 600 travel apps have emerged.
Cyclobutadiene is one of those small iconic molecules, the transience and instability of which was explained theoretically long before it was actually detected in 1965.[cite]10.1021/ja01092a049[/cite] Given that instability, I was intrigued as to how many crystal structures might have been reported for this ring system, along with the rather more stable congener cyclo-octatetraene. Here is what I found.
The thread thus far. The post about Na 2 He introduced the electride anionic counter-ion to Na + as corresponding topologically to a rare feature known as a non-nuclear attractor. This prompted speculation about other systems with such a feature, and the focus shifted to a tetrahedral arrangement of four hydrogen atoms as a dication, sharing a total of two valence electrons. The story now continues here.
This post arose from a comment attached to the post on Na 2 He and relating to peculiar and rare topological features of the electron density in molecules called non-nuclear attractors. This set me thinking about other molecules that might exhibit this and one of these is shown below.
I analysed the bonding in chlorine trifluoride a few years back in terms of VSEPR theory. I noticed that several searches on this topic which led people to this post also included a query about the differences between it and the bromine analogue. For those who posed this question, here is an equivalent analysis.