Posts Tagged ‘crystallography’

π-Facial hydrogen bonds to alkenes (revisited): how close can an acidic hydrogen approach?

Saturday, April 15th, 2017
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Back in the early 1990s, we first discovered the delights of searching crystal structures for unusual bonding features.[1] One of the first cases was a search for hydrogen bonds formed to the π-faces of alkenes and alkynes. In those days the CSD database of crystal structures was a lot smaller (<80,000 structures; it’s now ten times larger) and the search software less powerful. So here is an update. 

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References

  1. H.S. Rzepa, M.H. Smith, and M.L. Webb, "A crystallographic AM1 and PM3 SCF-MO investigation of strong OH ⋯π-alkene and alkyne hydrogen bonding interactions", J. Chem. Soc., Perkin Trans. 2, pp. 703-707, 1994. http://dx.doi.org/10.1039/P29940000703

To be cyclobutadiene, or not to be, that is the question? You decide.

Thursday, March 21st, 2013
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A quartet of articles has recently appeared on the topic of cyclobutadiene.[1],[2],[3],[4]. You will find a great deal discussed there, but I can boil it down to this essence. Do the following coordinates (obtained from a (disordered) previously published[5] x-ray refinement) correspond to a van der Waals complex of 1,3-dimethyl cyclobutadiene and carbon dioxide, or do they instead represent a covalent interaction between these two components resulting in a compound with the chemical name 2-oxabicyclo[2.2.0]hex-5-en-3-one (i.e. not a cyclobutadiene)?

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References

  1. H.S. Rzepa, "A Computational Evaluation of the Evidence for the Synthesis of 1,3-Dimethylcyclobutadiene in the Solid State and Aqueous Solution", Chemistry - A European Journal, vol. 19, pp. 4932-4937, 2013. http://dx.doi.org/10.1002/chem.201102942
  2. M. Shatruk, and I.V. Alabugin, "Reinvestigation of “Single-Crystal X-ray Structure of 1,3-dimethylcyclobutadiene”", Chemistry - A European Journal, vol. 19, pp. 4942-4945, 2013. http://dx.doi.org/10.1002/chem.201103017
  3. Y. Legrand, D. Dumitrescu, A. Gilles, E. Petit, A. van der Lee, and M. Barboiu, "A Constrained Disorder Refinement: “Reinvestigation of “Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene” by M. Shatruk and I. V. Alabugin”", Chemistry - A European Journal, vol. 19, pp. 4946-4950, 2013. http://dx.doi.org/10.1002/chem.201203234
  4. Y. Legrand, D. Dumitrescu, A. Gilles, E. Petit, A. van der Lee, and M. Barboiu, "Reply to A Computational Evaluation of the Evidence for the Synthesis of 1,3-Dimethylcyclobutadiene in Solid State and Aqueous Solution-Beyond the Experimental Reality", Chemistry - A European Journal, vol. 19, pp. 4938-4941, 2013. http://dx.doi.org/10.1002/chem.201203235
  5. Y. Legrand, A. van der Lee, and M. Barboiu, "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix", Science, vol. 329, pp. 299-302, 2010. http://dx.doi.org/10.1126/science.1188002