Archive for the ‘Interesting chemistry’ Category

Enantioselective epoxidation of alkenes using the Shi Fructose-based catalyst. An undergraduate experiment.

Tuesday, April 15th, 2014

The journal of chemical education can be a fertile source of ideas for undergraduate student experiments. Take this procedure for asymmetric epoxidation of an alkene.[1] When I first spotted it, I thought not only would it be interesting to do in the lab, but could be extended by incorporating some modern computational aspects as well. 

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References

  1. A. Burke, P. Dillon, K. Martin, and T.W. Hanks, "Catalytic Asymmetric Epoxidation Using a Fructose-Derived Catalyst", J. Chem. Educ., vol. 77, pp. 271, 2000. http://dx.doi.org/10.1021/ed077p271

Artemisinin: are stereo-electronics at the core of its (re)activity?

Sunday, April 13th, 2014

Around 100 tons of the potent antimalarial artemisinin is produced annually; a remarkable quantity given its very unusual and fragile looking molecular structure (below). When I looked at this, I was immediately struck by a thought: surely this is a classic molecule for analyzing stereoelectronic effects (anomeric and gauche). Here this aspect is explored.

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A connected world (journals and blogs): The benzene dication.

Thursday, April 10th, 2014

Science is rarely about a totally new observation or rationalisation, it is much more about making connections between known facts, and perhaps using these connections to extrapolate to new areas (building on the shoulders of giants, etc). So here I chart one example of such connectivity over a period of six years.

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Aromatic electrophilic substitution. A different light on the bromination of benzene.

Wednesday, March 12th, 2014

My previous post related to the aromatic electrophilic substitution of benzene using as electrophile phenyl diazonium chloride. Another prototypical reaction, and again one where benzene is too inactive for the reaction to occur easily, is the catalyst-free bromination of benzene to give bromobenzene and HBr. 

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A congruence of concepts: conformations, configurations, amides and enzymes

Sunday, February 9th, 2014

This is the time of year when I deliver two back-2-back lecture courses, and yes I do update and revise the content! I am always on the look-out for nice new examples that illustrate how concepts and patterns in chemistry can be joined up to tell a good story. My attention is currently on conformational analysis; and here is an interesting new story to tell about it.

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Three-for-one: a pericyclic brain teaser.

Sunday, January 12th, 2014

A game one can play with pericyclic reactions is to ask students to identify what type a given example is. So take for example the reaction below.

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Does forming a Wheland intermediate disrupt all aromaticity?

Friday, December 6th, 2013

Text books will announce that during aromatic electrophilic substitution, aromaticity is lost by the formation of a Wheland intermediate (and regained by eliminating a proton). Is that entirely true?wheland

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Caesium trifluoride: could it be made?

Saturday, November 23rd, 2013

Mercury (IV) tetrafluoride attracted much interest when it was reported in 2007[1] as the first instance of the metal being induced to act as a proper transition element (utilising d-electrons for bonding) rather than a post-transition main group metal (utilising just s-electrons) for which the HgF2 dihalide would be more normal (“Is mercury now a transition element?”[2]). Perhaps this is the modern equivalent of transmutation! Well, now we have new speculation about how to induce the same sort of behaviour for caesium; might it form CsF3 (at high pressures) rather than the CsF we would be more familiar with.[3] Here I report some further calculations inspired by this report.

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References

  1. X. Wang, L. Andrews, S. Riedel, and M. Kaupp, "Mercury Is a Transition Metal: The First Experimental Evidence for HgF4", Angew. Chem. Int. Ed., vol. 46, pp. 8371-8375, 2007. http://dx.doi.org/10.1002/anie.200703710
  2. W.B. Jensen, "Is Mercury Now a Transition Element?", J. Chem. Educ., vol. 85, pp. 1182, 2008. http://dx.doi.org/10.1021/ed085p1182
  3. M. Miao, "Caesium in high oxidation states and as a p-block element", Nature Chem, vol. 5, pp. 846-852, 2013. http://dx.doi.org/10.1038/nchem.1754

The subtle effect of dispersion forces on the shapes of molecules: benzyl magnesium bromide.

Sunday, November 10th, 2013

In the previous post I mentioned in passing the Grignard reagent benzyl magnesium bromide as having tetrahedral coordination at Mg. But I have now noticed, largely through spotting Steve Bachrach’s post on “Acene dimers – open or closed?” another geometric effect perhaps worthy of note, certainly one not always noted in the past; that of dispersion forces.

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Multiple personalities of Magnesium.

Tuesday, November 5th, 2013

The following is a short question in a problem sheet associated with introductory organic chemistry.

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