Henry Rzepa's Blog Chemistry with a twist

June 26, 2014

Amides and inverting the electronics of the Bürgi–Dunitz trajectory.

The Bürgi–Dunitz angle describes the trajectory of an approaching nucleophile towards the carbon atom of a carbonyl group. A colleague recently came to my office to ask about the inverse, that is what angle would an electrophile approach (an amide)? Thus it might approach either syn or anti with respect to the nitrogen, which is a feature not found with nucleophilic attack. amide My first thought was to calculate the wavefunction and identify the location and energy (= electrophilicity) of the lone pairs (the presumed attractor of an electrophile). But a better more direct approach soon dawned. A search of the crystal structure database. Here is the search definition, with the C=O-E angle, the O-E distance and the N-C=O-E torsion defined (also specified for R factor < 5%, no errors and no disorder). search   The first plot is of the torsion vs the distance, for E = H-X (X=O,F, Cl) amides

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April 10, 2014

A connected world (journals and blogs): The benzene dication.

Filed under: Hypervalency,Interesting chemistry — Tags: , , , — Henry Rzepa @ 10:56 am

Science is rarely about a totally new observation or rationalisation, it is much more about making connections between known facts, and perhaps using these connections to extrapolate to new areas (building on the shoulders of giants, etc). So here I chart one example of such connectivity over a period of six years.

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June 5, 2013

Computers 1967-2013: a personal perspective. Part 5. Network bandwidth.

In a time of change, we often do not notice that Δ = ∫δ. Here I am thinking of network bandwidth, and my personal experience of it over a 46 year period.

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