Henry Rzepa's Blog Chemistry with a twist

April 17, 2017

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

Filed under: crystal_structure_mining — Tags: , , , , — Henry Rzepa @ 8:13 am

Following on from my re-investigation of close hydrogen bonding contacts to the π-face of alkenes, here now is an updated scan for H-bonds to alkynes. The search query (dataDOI: 10.14469/hpc/2478) is similar to the previous one:

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June 13, 2016

A wider look at π-complex metal-alkene (and alkyne) compounds.

Previously, I looked at the historic origins of the so-called π-complex theory of metal-alkene complexes. Here I follow this up with some data mining of the crystal structure database for such structures.

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May 12, 2015

The Bürgi–Dunitz angle revisited: a mystery?

The Bürgi–Dunitz angle is one of those memes that most students of organic chemistry remember. It hypothesizes the geometry of attack of a nucleophile on a trigonal unsaturated (sp2) carbon in a molecule such as ketone, aldehyde, ester, and amide carbonyl. Its value obviously depends on the exact system, but is generally taken to be in the range 105-107°. A very good test of this approach is to search the crystal structure database (this was how it was originally established[1]).

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References

  1. H. B:urgi, J. Dunitz, J. Lehn, and G. Wipff, "Stereochemistry of reaction paths at carbonyl centres", Tetrahedron, vol. 30, pp. 1563-1572, 1974. http://dx.doi.org/10.1016/S0040-4020(01)90678-7

September 4, 2011

Anatomy of a simple reaction: the hydration of an alkene.

Filed under: Uncategorised — Tags: , , , , , — Henry Rzepa @ 6:33 pm

The hydration of an alkene by an acid is one of those fundamental reactions, taught early on in most chemistry courses. What can quantum mechanics teach us about the mechanism of the reaction?

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