Archive for the ‘Interesting chemistry’ Category
Thursday, July 18th, 2013
This potential example of a molecule on the edge of chaos was suggested to me by a student (thanks Stephen!), originating from an inorganic tutorial. It represents a class of Mo-complex ligated by two dithiocarbamate ligands and two aryl nitrene ligands (Ar-N:).
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Posted in Interesting chemistry | 2 Comments »
Thursday, July 11th, 2013
The butterfly effect summarises how a small change to a system may result in very large and often unpredictable (chaotic) consequences. If the system is merely on the edge of chaos, the consequences are predictable, but nevertheless finely poised between e.g. two possible outcomes. Here I ask how a molecule might manifest such behaviour.
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Posted in Interesting chemistry | 5 Comments »
Monday, July 8th, 2013
A feature of a blog which is quite different from a journal article is how rapidly a topic might evolve. Thus I started a few days ago with the theme of dicarbon (C2), identifying a metal carbide that showed C2 as a ligand, but which also entrapped a single carbon in hexa-coordinated mode. A comment was posted bringing attention to the origins of the discovery of hexacoordinated carbon, and we moved on to exploring the valency in one such species (CLi6). Here I ask if hydrogen itself might exhibit such coordination.
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Tags:chemical shift, metal atoms, metal carbide
Posted in Hypervalency, Interesting chemistry | 2 Comments »
Friday, July 5th, 2013
A comment made on the previous post on the topic of hexa-coordinate carbon cited an article entitled “Observation of hypervalent CLi6 by Knudsen-effusion mass spectrometry“[cite]10.1038/355432a0[/cite] by Kudo as a amongst the earliest of evidence that such species can exist (in the gas phase). It was a spectacular vindication of the earlier theoretical prediction[cite]10.1021/ja00379a051[/cite],[cite]10.1021/ja00356a045[/cite] that such 6-coordinate species are stable with respect to dissociation to CLi4 and Li2.
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Tags:energy, gas phase, Knudsen, low energy 2s/2p carbon, metal-metal bonding, pence
Posted in Hypervalency, Interesting chemistry | 7 Comments »
Wednesday, July 3rd, 2013
C2 (dicarbon) is certainly interesting from a theoretical point of view. Whether or not it can be described as having a quadruple bond has induced much passionate discussion[cite]10.1038/nchem.1263[/cite],[cite]10.1002/anie.201208206[/cite],[cite]10.1002/anie.201301485[/cite],[cite]10.1002/anie.201302350[/cite]. Its occurrence in space and in flames is also well-known. But does it have what might be called a conventional chemistry? Other highly reactive species (cyclobutadiene is a well-known example) can often be tamed by trapping as a ligand coordinated to a metal and so one might speculate upon how C2 responds to the proximity of a metal. As is noted here[cite]10.1002/anie.201208206[/cite], dicarbon as a ligand has been known a long time as part of what is referred to as carbide chemistry. In this regard it is thought of as the di-anion, C22- (and isoelectronic therefore with dinitrogen). Thus calcium carbide, but in fact the degree to which the dicarbon can absorb electrons is thought to be wide (as judged by the resulting C-C bond length, see[cite]10.1002/anie.201208206[/cite]). Here I take a look at just one metal carbide[cite]10.1016/j.jssc.2008.08.005[/cite] that caught my eye (there are hundreds of others, many no doubt equally interesting!).
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Tags:metal, metal coordinating, Os-C
Posted in Interesting chemistry | 6 Comments »
Wednesday, June 26th, 2013
A reader asked me about the mechanism of the reaction of 2-picoline N-oxide with acetic anhydride to give 2-acetoxymethylpyridine (the Boekelheide Rearrangement[cite]10.1002/ejoc.201000936[/cite]). He wrote ” I don’t understand why the system should prefer to go via fragmentation-recombination (… the evidence being that oxygen labelling shows scrambling) when there is an easy concerted pathway available (… a [3,3]sigmatropic shift). Furthermore, is it possible for two pathways to co-exist?” Here is how computation might enlighten us.
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Tags:ATM, CF 3 CO, CH 3 CO, extraneous product, free energy, free energy barrier, recombination
Posted in Interesting chemistry, pericyclic, reaction mechanism | 3 Comments »
Friday, May 24th, 2013
The title of this post comes from a comment posted by Ryan, who asks about isocyanide’s role (in the form of the anion of tosyl isocyanide, or TosMIC) in two named reactions, Van Leusen and Ugi FCR. “In Van Leusen, it (the isocyanide) acts as an electrophile: however, in Ugi, it acts as a nucleophile”. Here are some valence bond forms for this species;
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Tags:Ugi, Van Leusen
Posted in Interesting chemistry | 2 Comments »
Wednesday, May 15th, 2013
In the preceding post, I introduced Dewar’s π-complex theory for alkene-metal compounds, outlining the molecular orbital analysis he presented, in which the filled π-MO of the alkene donates into a Ag+ empty metal orbital and back-donation occurs from a filled metal orbital into the alkene π* MO. Here I play a little “what if” game with this scenario to see what one can learn from doing so.
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Tags:African Union, alkene-metal compounds, empty metal orbital, energy, filled metal orbital, free energy, Historical, lower energy form, metal
Posted in Hypervalency, Interesting chemistry | 1 Comment »