Posts Tagged ‘Molecular geometry’

How does methane invert (its configuration)?

Thursday, March 16th, 2017
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This is a spin-off from the table I constructed here for further chemical examples of the classical/non-classical norbornyl cation conundrum. One possible entry would include the transition state for inversion of methane via a square planar geometry as compared with e.g. NiH4 for which the square planar motif is its minimum. So is square planar methane a true transition state for inversion (of configuration) of carbon?

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The smallest C-C-C angle?

Monday, October 31st, 2016
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Is asking a question such as “what is the smallest angle subtended at a chain of three connected 4-coordinate carbon atoms” just seeking another chemical record, or could it unearth interesting chemistry?

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The geometries of 5-coordinate compounds of group 14 elements.

Monday, May 30th, 2016
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This is a follow-up to one aspect of the previous two posts dealing with nucleophilic substitution reactions at silicon. Here I look at the geometries of 5-coordinate compounds containing as a central atom 4A = Si, Ge, Sn, Pb and of the specific formula C34AO2 with a trigonal bipyramidal geometry. This search arose because of a casual comment I made in the earlier post regarding possible cooperative effects between the two axial ligands (the ones with an angle of ~180 degrees subtended at silicon). Perhaps the geometries might expand upon this comment?

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The mechanism of silylether deprotection using a tetra-alkyl ammonium fluoride.

Wednesday, May 25th, 2016
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The substitution of a nucleofuge (a good leaving group) by a nucleophile at a carbon centre occurs with inversion of configuration at the carbon, the mechanism being known by the term SN2 (a story I have also told in this post). Such displacement at silicon famously proceeds by a quite different mechanism, which I here quantify with some calculations.

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Bond stretch isomerism. Did this idea first surface 100 years ago?

Tuesday, February 9th, 2016
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The phenomenon of bond stretch isomerism, two isomers of a compound differing predominantly in just one bond length, is one of those chemical concepts that wax and occasionally wane.[1] Here I explore such isomerism for the elements Ge, Sn and Pb.

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References

  1. J.A. Labinger, "Bond-stretch isomerism: a case study of a quiet controversy", Comptes Rendus Chimie, vol. 5, pp. 235-244, 2002. http://dx.doi.org/10.1016/S1631-0748(02)01380-2

VSEPR Theory: A closer look at trifluorothionitrile, NSF3.

Saturday, January 16th, 2016
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The post on applying VSEPR ("valence shell electron pair repulsion") theory to the geometry of ClF3 has proved perennially popular. So here is a follow-up on another little molecue, F3SN. As the name implies, it is often represented with an S≡N bond. Here I take a look at the conventional analysis.

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