Posts Tagged ‘energy’
Tuesday, April 2nd, 2013
My previous dissection of the mechanism for ester hydrolysis dealt with the acyl-oxygen cleavage route (red bond). There is a much rarer[1] alternative: alkyl-oxygen cleavage (green bond) which I now place under the microscope.
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References
- C.A. Bunton, and J.L. Wood, "Tracer studies on ester hydrolysis. Part II. The acid hydrolysis of tert.-butyl acetate", Journal of the Chemical Society (Resumed), pp. 1522, 1955. https://doi.org/10.1039/jr9550001522
Tags:acetic acid, analogous energy, energy, lower energy route, Reaction Mechanism, Tutorial material
Posted in Uncategorised | 3 Comments »
Friday, March 29th, 2013
The mechanism of ester hydrolysis is a staple of examination questions in organic chemistry. To get a good grade, one might have to reproduce something like the below. Here, I subject that answer to a reality check.
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Tags:ALSO, co-operative, energy, energy well, ester hydrolysis, free energy, Reaction Mechanism, shallow energy, solvation energy, Tutorial material
Posted in Uncategorised | 16 Comments »
Sunday, March 3rd, 2013
The electrophilic substitution of indoles is a staple of any course on organic chemistry. Indoles also hold a soft-spot for me, since I synthesized not a few as part of my Ph.D. studies.[1],[2] The preference for substitution in the 3-position is normally explained using the arrows shown below (position 3=green,2=blue,1=red). Here I explore how these arrows might be interpreted in terms of various quantum mechanical properties.
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References
- B.C. Challis, and H.S. Rzepa, "The mechanism of diazo-coupling to indoles and the effect of steric hindrance on the rate-limiting step", Journal of the Chemical Society, Perkin Transactions 2, pp. 1209, 1975. https://doi.org/10.1039/p29750001209
- B.C. Challis, and H.S. Rzepa, "Heteroaromatic hydrogen exchange reactions. Part 9. Acid catalysed decarboxylation of indole-3-carboxylic acids", Journal of the Chemical Society, Perkin Transactions 2, pp. 281, 1977. https://doi.org/10.1039/p29770000281
Tags:benzo, energy, least-favourable energy, lowest energy gap, Reaction Mechanism, reaction product, Tutorial material
Posted in Interesting chemistry | 2 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, steric exchange energy, Tutorial material
Posted in crystal_structure_mining, Interesting chemistry | 1 Comment »
Friday, January 25th, 2013
Although have dealt with the π-complex formed by protonation of PhNHOPh in several posts, there was one aspect that I had not really answered; what is the most appropriate description of its electronic nature? Here I do not so much provide an answer, as try to show how difficult getting an accurate answer might be.
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Tags:electronic energy, energy, multi-reference solution
Posted in Interesting chemistry | No Comments »
Friday, January 18th, 2013
Michael Dewar[1] famously implicated a so-called π-complex in the benzidine rearrangement, back in the days when quantum mechanical calculations could not yet provide a quantitatively accurate reality check. Because this π-complex actually remains a relatively unusual species to encounter in day-to-day chemistry, I thought I would try to show in a simple way how it forms.
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References
- M. Dewar, and H. McNicoll, "Mechanism of the benzidine rearrangement", Tetrahedron Letters, vol. 1, pp. 22-23, 1959. https://doi.org/10.1016/s0040-4039(01)82765-9
Tags:energy, high energy molecules, Michael Dewar, Reaction Mechanism
Posted in Interesting chemistry | 2 Comments »
Wednesday, January 16th, 2013
If you search e.g. Scifinder for N,O-diphenyl hydroxylamine (RN 24928-98-1) there is just one literature citation, to a 1962 patent. Nothing else; not even a calculation (an increasing proportion of the molecules reported in Chemical Abstracts have now only ever been subjected to calculation, not synthesis). A search of Reaxys also offers only one hit[1] reporting one unsuccessful attempt in 1963 to prepare this compound. Again, nothing else. Yet show this structure to most organic chemists, and I venture to suggest few would immediately predict this (unless they are experts on benzidine rearrangements).‡
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References
- J.R. Cox, and M.F. Dunn, "The chemistry of O,N-diarylhydroxlamines - I", Tetrahedron Letters, vol. 4, pp. 985-989, 1963. https://doi.org/10.1016/s0040-4039(01)90757-9
Tags:energy, Historical, metal, pericyclic, Reaction Mechanism
Posted in Interesting chemistry | 7 Comments »