Archive for the ‘Chemical IT’ Category

Could anyone comment on any recent calculated results on the planarity, or lack thereof, of azobenzene?

Sunday, December 20th, 2015

This question was posted on the CCL (computational chemistry list) by John McKelvey. Here, I give an answer in the form of a search of the CSD (crystal structure database).

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Deviations from planarity of trigonal carbon and from linearity of digonal carbon.

Sunday, September 13th, 2015

Previously, I explored deviation from ideal tetrahedral arrangements of four carbon ligands around a central (sp3) carbon using crystal structures. Now it is the turn of digonal (sp1) and trigonal (sp2) carbons. 

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Deviations from tetrahedral four-coordinate carbon: a statistical exploration.

Sunday, September 6th, 2015

An article entitled "Four Decades of the Chemistry of Planar Hypercoordinate Compounds"[1] was recently reviewed by Steve Bacharach on his blog, where you can also see comments. Given the recent crystallographic themes here, I thought I might try a search of the CSD (Cambridge structure database) to see whether anything interesting might emerge for tetracoordinate carbon.

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References

  1. L. Yang, E. Ganz, Z. Chen, Z. Wang, and P.V.R. Schleyer, "Four Decades of the Chemistry of Planar Hypercoordinate Compounds", Angewandte Chemie International Edition, vol. 54, pp. 9468-9501, 2015. https://doi.org/10.1002/anie.201410407

π-Resonance in thioamides: a crystallographic “diff” with amides.

Saturday, September 5th, 2015

The previous post explored the structural features of amides. Here I compare the analysis with that for the closely related thioamides.

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π-Resonance in amides: a crystallographic reality check.

Saturday, September 5th, 2015

The π-resonance in amides famously helped Pauling to his proposal of a helical structure for proteins. Here I explore some geometric properties of amides related to the C-N bond and the torsions about it.

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A sea-change in science citation? The Wikipedia Science conference.

Thursday, September 3rd, 2015

The first conference devoted to scientific uses of Wikipedia has just finished; there was lots of fascinating stuff but here I concentrate on one report that I thought was especially interesting. To introduce it, I need first to introduce WikiData. This is part of the WikiMedia ecosystem, and one of the newest. The basic concept is really simple.

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A visualization of the anomeric effect from crystal structures.

Thursday, August 27th, 2015

The anomeric effect is best known in sugars, occuring in sub-structures such as RO-C-OR. Its origins relate to how the lone pairs on each oxygen atom align with the adjacent C-O bonds. When the alignment is 180°, one oxygen lone pair can donate into the C-O σ* empty orbital and a stabilisation occurs. Here I explore whether crystal structures reflect this effect.

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Mesomeric resonance in substituted benzenes: a crystallographic reality check.

Wednesday, August 26th, 2015

Previously, I showed how conjugation in dienes and diaryls can be visualised by inspecting bond lengths as a function of torsions. Here is another illustration, this time of the mesomeric resonance on a benzene ring induced by an electron donating substituent (an amino group) or an electron withdrawing substituent (cyano).

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A visualisation of the effects of conjugation; dienes and biaryls.

Tuesday, August 25th, 2015

Here is another exploration of simple chemical concepts using crystal structures. Consider a simple diene: how does the central C-C bond length respond to the torsion angle between the two C=C bonds?

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A (light) introductory tutorial on Research Data Management (in chemistry).

Thursday, August 20th, 2015

Management of research (data) outputs is a hot topic in the UK at the moment, although the topic has been rumbling for five years or more. Most research-active higher educational establishments have or are about to publish general guidelines, which predominantly take the form of aspirational targets rather than actionable examples or use-cases. Because the concepts remain somewhat abstract, one can encounter questions from researchers such as “how should I go about achieving such RDM (research data management)?” I thought it might be useful for me to here summarise some key features in the form of an FAQ that can help answer that question. I will concentrate purely on the sub-set chemistry about which I know most.

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