Posts Tagged ‘conformational analysis’
Sunday, March 17th, 2013
n-Butyl lithium is hexameric in the solid state[1] and in cyclohexane solutions. Why? Here I try to find out some of its secrets.
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References
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T. Kottke, and D. Stalke, "Structures of Classical Reagents in Chemical Synthesis:(nBuLi)6,(tBuLi)4, and the Metastable(tBuLi· Et2O)2", Angewandte Chemie International Edition in English, vol. 32, pp. 580-582, 1993. http://dx.doi.org/10.1002/anie.199305801
Tags:Cambridge, chemical shifts, conformational analysis, cyclohexane solutions, hexameric, Interesting chemistry, spherical aromaticity, Tutorial material
Posted in Uncategorised | 16 Comments »
Monday, February 11th, 2013
This is really just a postscript to the previous post. There I showed how a search of the (small molecule) crystal database revealed the s-cis conformation about the N-C amide bond (the one with partial double bond character that prevents rotation) and how this conformation means that a C-H approaches quite closely to an adjacent oxygen. It is a tiny step from that search to a related, and very famous one named after Ramachandran[1]. Indeed this search, and the contour map used to display the results, really put crystal databases on the map so to speak.
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References
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G. Ramachandran, C. Ramakrishnan, and V. Sasisekharan, "Stereochemistry of polypeptide chain configurations", Journal of Molecular Biology, vol. 7, pp. 95-99, 1963. http://dx.doi.org/10.1016/S0022-2836(63)80023-6
Tags:conformational analysis, Interesting chemistry, search above, Tutorial material
Posted in Uncategorised | No Comments »
Friday, February 8th, 2013
Consider acetaldehyde (ethanal for progressive nomenclaturists). What conformation does it adopt, and why? This question was posed of me by a student at the end of a recent lecture of mine. Surely, an easy answer to give? Read on …
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Tags:Cambridge, conformational analysis, energy, free energy, Interesting chemistry, steric exchange energy, Tutorial material
Posted in crystal_structure_mining | 1 Comment »
Sunday, February 3rd, 2013
The electronic interaction between a single bond and an adjacent double bond is often called σ-π-conjugation (an older term for this is hyperconjugation), and the effect is often used to e.g. explain why more highly substituted carbocations are more stable than less substituted ones. This conjugation is more subtle in neutral molecules, but following my use of crystal structures to explore the so-called gauche effect (which originates from σ-σ-conjugation), I thought I would have a go here at seeing what the crystallographic evidence actually is for the σ-π-type.
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Tags:above search, Cambridge, conformational analysis, Interesting chemistry, Tutorial material, X-ray
Posted in crystal_structure_mining | 1 Comment »
Sunday, January 13th, 2013
We tend to think of simple hydrocarbons as relatively inert and un-interesting molecules. However, a recent article[1], which was in fact highlighted by Steve Bachrach on his blog , asks what “The Last Globally Stable Extended Alkane” might be. In other words, at what stage does a straight-chain hydrocarbon fold back upon itself, and no significant population of the linear form remain? The answer was suggested to be C17H36. I thought I might subject this conformation to an NCI (non-covalent-interaction) analysis.
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References
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N.O.B. Lüttschwager, T.N. Wassermann, R.A. Mata, and M.A. Suhm, "The Last Globally Stable Extended Alkane", Angewandte Chemie International Edition, vol. 52, pp. 463-466, 2012. http://dx.doi.org/10.1002/anie.201202894
Tags:conformational analysis, Steve Bachrach, Tutorial material
Posted in Uncategorised | 5 Comments »
Friday, January 4th, 2013
Tags:basic search, Cambridge, CF 3, conformational analysis, gauche, Interesting chemistry, metal, search takes, similar, Tutorial material
Posted in crystal_structure_mining | 8 Comments »