Comments on: Ring-flipping in cyclohexane in a different light

By: Henry Rzepa

Henry Rzepa — Fri, 12 Oct 2012 20:06:09 +0000

One can indeed construct permutational maps connecting all possible half-chairs with paths to twist boats etc. It is indeed a complex hypersurface.

Hermann Sachse is indeed an interesting figure (I mentioned him and planar cyclohexane in an earlier blog). He used trigonometry to prove his theory, something that quite failed to get the message across to an audience of organic chemists.

By: Paul Schleyer

Paul Schleyer — Fri, 12 Oct 2012 18:57:50 +0000

Still more elaborate depictions of the cyclohexane PES I have seen include the pseudororational interconversion of all the possible equivalent {“labelled”] C2v and D2 conformers and enantiomers in the center. Of course, there are many more C2 conformers are well.

Although it has 3 imaginary frequencies, planar D6h cyclohexane is of historical interest. since it was the geometry von Baeyer considered in his famous strain paper of 1884. Although refuted by Sachse (see Wilkipedia for wonderful details), Baeyer believed cyclohexane was planar to his dying day.

Since D3d (chair) cyclohexane is highly stabilized (about 17 kcal/mol) by six protobranches, it is should NOT be used as a model “strain-free” molecule.

By: The conformation of cyclohexane « Henry Rzepa

The conformation of cyclohexane « Henry Rzepa — Fri, 12 Oct 2012 14:26:13 +0000

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