Posts Tagged ‘chemical synthesis’

Feist’s acid. Stereochemistry galore.

Thursday, April 4th, 2013
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Back in the days (1893) when few compounds were known, new ones could end up being named after the discoverer. Thus Feist is known for the compound bearing his name; the 2,3 carboxylic acid of methylenecyclopropane (1, with Me replaced by CO2H). Compound 1 itself nowadays is used to calibrate chiroptical calculations[1], which is what brought it to my attention. But about four decades ago, and now largely forgotten, both 1 and the dicarboxylic acid were famous for the following rearrangement that gives a mixture of 2 and 3[2]. I thought I might here unpick some of the wonderfully subtle stereochemical analysis that this little molecule became subjected to.
methylene-cyclopropane

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References

  1. E.D. HedegÄrd, F. Jensen, and J. Kongsted, "Basis Set Recommendations for DFT Calculations of Gas-Phase Optical Rotation at Different Wavelengths", Journal of Chemical Theory and Computation, vol. 8, pp. 4425-4433, 2012. http://dx.doi.org/10.1021/ct300359s
  2. J.J. Gajewski, "Hydrocarbon thermal degenerate rearrangements. IV. Stereochemistry of the methylenecyclopropane self-interconversion. Chiral and achiral intermediates", Journal of the American Chemical Society, vol. 93, pp. 4450-4458, 1971. http://dx.doi.org/10.1021/ja00747a019

Perbromate. A riddle, wrapped in a mystery, inside an enigma; but perhaps there is a key.

Friday, April 6th, 2012
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Chemists love a mystery as much as anyone. And gaps in patterns can be mysterious. Mendeleev’s period table had famous gaps which led to new discovery. And so from the 1890s onwards, chemists searched for the perbromate anion, BrO4. It represented a gap between perchlorate and periodate, both of which had long been known. As the failure to turn up perbromate persisted, the riddle deepened. Finally, in 1968, the key was found, but talk about sledgehammer to crack a nut! It was done by alchemical-like radioactive transmutation of selenium into bromine:

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