Posts Tagged ‘Tutorial material’
Thursday, January 31st, 2013
It is always rewarding when one comes across a problem in chemistry that can be solved using a continuous stream of rules and logical inferences from them. The example below[1] is one I have been using as a tutor in organic chemistry for a few years now, and I share it here. It takes around 50 minutes to unravel with students.
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References
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K. Harano, M. Eto, K. Ono, K. Misaka, and T. Hisano, "Sequential pericyclic reactions of unsaturated xanthates. One-pot synthesis of hydrobenzo[c]thiophenes", Journal of the Chemical Society, Perkin Transactions 1, pp. 299, 1993. http://dx.doi.org/10.1039/P19930000299
Tags:final product, pericyclic, tutor, Tutorial material
Posted in Uncategorised | 2 Comments »
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 »
Thursday, January 3rd, 2013
One frequently has to confront the question: will a hydrogen bond form between a suitable donor (lone pair or π) and an acceptor? One of the factors to be taken into consideration for hydrogen bonds which are part of a cycle is the ring size. Here I explore one way of quantifying the effect for the series below, n=1-5 (4-8 membered rings).
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Tags:Cambridge, energy, energy gap, interaction energy, Interesting chemistry, Tutorial material
Posted in Uncategorised | 2 Comments »
Thursday, January 3rd, 2013
I return to this reaction one more time. Trying to explain why it is enantioselective for the epoxide product poses peculiar difficulties. Most of the substituents can adopt one of several conformations, and some exploration of this conformational space is needed.
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Tags:catalysis, conformational analysis, energy, epoxide product, free energy, Interesting chemistry, Reaction Mechanism, similar systems, Tutorial material
Posted in Uncategorised | No Comments »
Monday, December 24th, 2012
tpap[1], as it is affectionately known, is a ruthenium-based oxidant of primary alcohols to aldehydes discovered by Griffith and Ley. Whereas ruthenium tetroxide (RuO4) is a voracious oxidant[2], its radical anion countered by a tetra-propylammonium cation is considered a more moderate animal[3]. In this post, I want to try to use quantum mechanically derived energies as a pathfinder for exploring what might be going on (or a reality-check if you like).
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References
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S.V. Ley, J. Norman, W.P. Griffith, and S.P. Marsden, "Tetrapropylammonium Perruthenate, Pr4N+RuO4
-, TPAP: A Catalytic Oxidant for Organic Synthesis", Synthesis, vol. 1994, pp. 639-666, 1994. http://dx.doi.org/10.1055/s-1994-25538
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D.G. Lee, U.A. Spitzer, J. Cleland, and M.E. Olson, "The oxidation of cyclobutanol by ruthenium tetroxide and sodium ruthenate", Canadian Journal of Chemistry, vol. 54, pp. 2124-2126, 1976. http://dx.doi.org/10.1139/v76-304
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D.G. Lee, Z. Wang, and W.D. Chandler, "Autocatalysis during the reduction of tetra-n-propylammonium perruthenate by 2-propanol", The Journal of Organic Chemistry, vol. 57, pp. 3276-3277, 1992. http://dx.doi.org/10.1021/jo00038a009
Tags:catalysis, energy, free energy, Interesting chemistry, low energy elimination, metal, react freq, Reaction Mechanism, RuO4+ ethanol, triplet state energy, Tutorial material
Posted in Uncategorised | 2 Comments »
Monday, December 17th, 2012
Part one on this topic showed how a quantum mechanical model employing just one titanium centre was not successful in predicting the stereochemical outcome of the Sharpless asymmetric epoxidation. Here in part 2, I investigate whether a binuclear model might have more success. The new model is constructed using two units of Ti(OiPr)4, which are likely to assemble into a dimer such as that shown below (in this crystal structure, some of the iPr groups are perfluorinated).
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Tags:catalysis, catalytic metal centre, Enantioselective, free energy difference, Interesting chemistry, Reaction Mechanism, Sharpless epoxidation, t-butyl, This free energy difference, Tutorial material
Posted in Uncategorised | 2 Comments »
Sunday, December 9th, 2012
Sharpless epoxidation converts a prochiral allylic alcohol into the corresponding chiral epoxide with > 90% enantiomeric excess[1],[2]. Here is the first step in trying to explain how this magic is achieved.
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References
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J.M. Klunder, S.Y. Ko, and K.B. Sharpless, "Asymmetric epoxidation of allyl alcohol: efficient routes to homochiral .beta.-adrenergic blocking agents", The Journal of Organic Chemistry, vol. 51, pp. 3710-3712, 1986. http://dx.doi.org/10.1021/jo00369a032
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R.M. Hanson, and K.B. Sharpless, "Procedure for the catalytic asymmetric epoxidation of allylic alcohols in the presence of molecular sieves", The Journal of Organic Chemistry, vol. 51, pp. 1922-1925, 1986. http://dx.doi.org/10.1021/jo00360a058
Tags:animation, asymmetric epoxidation, catalysis, Enantioselective, free energy, Interesting chemistry, lower energy conformations, Reaction Mechanism, Tutorial material
Posted in Uncategorised | 1 Comment »
