The largest C-C-C angle?

I am now inverting the previous question by asking what is the largest angle subtended at a chain of three connected 4-coordinate carbon atoms? Let’s see if further interesting chemistry can be unearthed.

Specifying only angles > 130°, the following distribution is obtained.

  • Note the maximum at ~138°. This is typical of that found in spiro-cyclopropanes, although I have not checked if other kinds of compound can also sustain this angle.
  • There appear to be a few examples at 180° but these appear to be simple errors in the crystal coordinates.
  • The first real example occurs at 166°[1] and contains an almost hemispherical carbon atom, doi: 10.5517/CCZBB2P [2]
  • A second example is a sprung spiro-cyclopropane [3] in which the large angle is maintained without the help of a metal.
  • This latter example suggests that a structural modification as shown below might take the angle to almost 180° (calc. ωB97XD/Def2-TZVPP = 177.2°[4]).

It is remarkable how much the standard angle subtended at four-coordinate carbon (109.47°) can be opened. It makes one wonder whether something approaching 180° is achievable, and what the properties of such a molecule might be.

 

References

  1. V. González-López, M.A. Leyva, and M.J. Rosales-Hoz, "Coupling of acetylene molecules on ruthenium clusters, involving cleavage of C–Si bonds in the alkyne and coordination of a phenyl ring of a SiPh3 group", Dalton Transactions, vol. 42, pp. 5401, 2013. http://dx.doi.org/10.1039/C3DT32335H
  2. R. Boese, D. Blaeser, K. Gomann, and U.H. Brinker, "Spiropentane as a tensile spring", Journal of the American Chemical Society, vol. 111, pp. 1501-1503, 1989. http://dx.doi.org/10.1021/ja00186a058
Henry Rzepa

Henry Rzepa is Emeritus Professor of Computational Chemistry at Imperial College London.

View Comments

  • Roald Hoffmann has sent me the following comment:

    "On large angles: Computationally, we found some in hypothetical prismane structures, attached (doi: 10.1021/jo034910l and 10.1021/om960099b) We also did an estimate of the energy to open up that angle in substituted methane, in another paper. The structure your search found are intriguing.

Recent Posts

Detecting anomeric effects in tetrahedral boron bearing four oxygen substituents.

In an earlier post, I discussed a phenomenon known as the "anomeric effect" exhibited by…

1 day ago

Internet Archeology: reviving a 2001 article published in the Internet Journal of Chemistry.

In the mid to late 1990s as the Web developed, it was becoming more obvious…

1 month ago

Detecting anomeric effects in tetrahedral carbon bearing four oxygen substituents.

I have written a few times about the so-called "anomeric effect", which relates to stereoelectronic…

1 month ago

Data Citation – a snapshot of the chemical landscape.

The recent release of the DataCite Data Citation corpus, which has the stated aim of…

2 months ago

Mechanistic templates computed for the Grubbs alkene-metathesis reaction.

Following on from my template exploration of the Wilkinson hydrogenation catalyst, I now repeat this…

2 months ago

3D Molecular model visualisation: 3 Million atoms +

In the late 1980s, as I recollected here the equipment needed for real time molecular…

3 months ago