Posts Tagged ‘energy’

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

Patterns of behaviour: serendipity in action for enantiomerisation of F-S-S-Cl

Thursday, September 19th, 2013

Paul Schleyer sent me an email about a pattern he had spotted, between my post on F3SSF and some work he and Michael Mauksch had done 13 years ago with the intriguing title “Demonstration of Chiral Enantiomerization in a Four-Atom Molecule“.[1] Let me explain the connection, but also to follow-up further on what I discovered in that post and how a new connection evolved.FSSF3-gen

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References

  1. P.V.R. Schleyer, and M. Mauksch, "Demonstration of Chiral Enantiomerization in a Four‐Atom Molecule ", Angewandte Chemie International Edition, 2000. http://doi.org/d8g2nw

Molecule-sized pixels.

Sunday, August 11th, 2013

The ultimate reduction in size for an engineer is to a single molecule. It’s been done for a car; now it has been reported for the pixel (picture-element).[1]

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References

  1. J.E. Kwon, S. Park, and S.Y. Park, "Realizing Molecular Pixel System for Full-Color Fluorescence Reproduction: RGB-Emitting Molecular Mixture Free from Energy Transfer Crosstalk", J. Am. Chem. Soc., vol. 135, pp. 11239-11246, 2013. http://dx.doi.org/10.1021/ja404256s

Is CLi6 hypervalent?

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[1] 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[2],[3] that such 6-coordinate species are stable with respect to dissociation to CLi4 and Li2.

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References

  1. H. Kudo, "Observation of hypervalent CLi6 by Knudsen-effusion mass spectrometry", Nature, vol. 355, pp. 432-434, 1992. http://dx.doi.org/10.1038/355432a0
  2. E.D. Jemmis, J. Chandrasekhar, E.U. Wuerthwein, P.V.R. Schleyer, J.W. Chinn, F.J. Landro, R.J. Lagow, B. Luke, and J.A. Pople, "Lithiated carbocations. The generation, structure, and stability of CLi5+", J. Am. Chem. Soc., vol. 104, pp. 4275-4276, 1982. http://dx.doi.org/10.1021/ja00379a051
  3. P.V.R. Schleyer, E.U. Wuerthwein, E. Kaufmann, T. Clark, and J.A. Pople, "Effectively hypervalent molecules. 2. Lithium carbide (CLi5), lithium carbide (CLi6), and the related effectively hypervalent first row molecules, CLi5-nHn and CLi6-nHn", J. Am. Chem. Soc., vol. 105, pp. 5930-5932, 1983. http://dx.doi.org/10.1021/ja00356a045

Woodward’s symmetry considerations applied to electrocyclic reactions.

Monday, May 20th, 2013

Sometimes the originators of seminal theories in chemistry write a personal and anecdotal account of their work. Niels Bohr[1] was one such and four decades later Robert Woodward wrote “The conservation of orbital symmetry” (Chem. Soc. Special Publications (Aromaticity), 1967, 21, 217-249; it is not online and so no doi can be given). Much interesting chemistry is described there, but (like Bohr in his article), Woodward lists no citations at the end, merely giving attributions by name. Thus the following chemistry (p 236 of this article) is attributed to a Professor Fonken, and goes as follows (excluding the structure in red):

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References

  1. N. Bohr, "Der Bau der Atome und die physikalischen und chemischen Eigenschaften der Elemente", Z. Physik, vol. 9, pp. 1-67, 1922. http://dx.doi.org/10.1007/BF01326955

Au and Pt π-complexes of cyclobutadiene.

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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Why diphenyl peroxide does not exist.

Monday, April 29th, 2013

A few posts back, I explored the “benzidine rearrangement” of diphenyl hydrazine. This reaction requires diprotonation to proceed readily, but we then discovered that replacing one NH by an O as in N,O-diphenyl hydroxylamine required only monoprotonation to undergo an equivalent facile rearrangement. So replacing both NHs by O to form diphenyl peroxide (Ph-O-O-Ph) completes this homologous series. I had speculated that PhNHOPh might exist if all traces of catalytic acid were removed, but could the same be done to PhOOPh? Not if it continues the trend and requires no prior protonation at all!

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How to predict the regioselectivity of epoxide ring opening.

Sunday, April 28th, 2013

I recently got an email from a student asking about the best way of rationalising epoxide ring opening using some form of molecule orbitals. This reminded me of the famous experiment involving propene epoxide.[1]

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References

  1. H.C. Chitwood, and B.T. Freure, "", J. Am. Chem. Soc., vol. 68, pp. 680-683, 1946. http://dx.doi.org/10.1021/ja01208a047

The mechanism of ester hydrolysis via alkyl oxygen cleavage under a quantum microscope

Tuesday, April 2nd, 2013

My previous dissection of the mechanism for ester hydrolysis dealt with the acyl-oxygen cleavage route (red bond). There is a much rarer[1] alternative: alkyl-oxygen cleavage (green bond) which I now place under the microscope.

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References

  1. C.A. Bunton, and J.L. Wood, "Tracer studies on ester hydrolysis. Part II. The acid hydrolysis of tert.-butyl acetate", J. Chem. Soc., pp. 1522, 1955. http://dx.doi.org/10.1039/jr9550001522

A sideways look at the mechanism of ester hydrolysis.

Friday, March 29th, 2013

The mechanism of ester hydrolysis is a staple of examination questions in organic chemistry. To get a good grade, one might have to reproduce something like the below. Here, I subject that answer to a reality check.

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