December 6th, 2011
My previous three posts set out my take on three principle categories of pericyclic reaction. Here I tell a prequel to the understanding of these reactions. In 1965, Woodward and Hoffmann[1] in their theoretical analysis (submitted Nov 30, 1964) for which the Nobel prize (to Hoffmann only of the pair, Woodward having died) was later awarded. But in the same year, Elias Corey[2] reported the conclusion of a project started several years earlier (first reported (DOI: 10.1021/ja00907a030, Nov 1, 1963) to synthesize the sesquiterpene dihydrocostunolide.
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References
- R.B. Woodward, and R. Hoffmann, "Stereochemistry of Electrocyclic Reactions", Journal of the American Chemical Society, vol. 87, pp. 395-397, 1965. https://doi.org/10.1021/ja01080a054
- E.J. Corey, and A.G. Hortmann, "The Total Synthesis of Dihydrocostunolide", Journal of the American Chemical Society, vol. 87, pp. 5736-5742, 1965. https://doi.org/10.1021/ja00952a037
Tags: electrocyclic, Elias Corey, Historical, pericyclic, photochemical, photochemical product, Tutorial material
Posted in Interesting chemistry | 2 Comments »
November 29th, 2011
Another common type of pericyclic reaction is the migration of hydrogen or carbon along a conjugated chain, as in the [1,3] migration of a carbon as shown below. As before, I explore the stereochemistry of the thermal and photochemical reactions.
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Tags: pericyclic, Tutorial material
Posted in Uncategorised | 1 Comment »
November 28th, 2011
Tags: energy, methyl, pericyclic, Tutorial material
Posted in Uncategorised | 2 Comments »
November 26th, 2011
Woodward and Hoffmann published their milestone article “Stereochemistry of Electrocyclic Reactions” in 1965. This brought maturity to the electronic theory of organic chemistry, arguably started by the proto-theory of Armstrong some 75 years earlier. Here, I take a modern look at the archetypal carrier of this insight, the ring opening of dimethylcyclobutene.
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Tags: Adam, archetypal carrier, conical intersections, electrocyclic, Historical, pericyclic, Tutorial material
Posted in Uncategorised | 1 Comment »
November 25th, 2011
In the previous post, I wrote about the processes that might be involved in a molecular wheel rotating. A nano car has four wheels, and surely the most amazing thing is how the wheels manage to move in synchrony. This is one hell of a tough problem, and I do not attempt an answer here, but simply record an odd observation.
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Tags: animation, nano car
Posted in Interesting chemistry | 2 Comments »
November 16th, 2011
The epoxidation of an alkene to give an oxirane is taught in introductory organic chemistry. Formulating an analogous mechanism for such reaction of an alkyne sounds straightforward, but one gradually realises that it requires raiding knowledge from several other areas of (perhaps slightly more advanced) chemistry to achieve a joined up approach to the problem. I had indeed hinted in a previous post that the mechanism for oxidation of acetylene to ketene might be an interesting arrow pushing challenge to set a bright tutorial group, and it was that self-hint that has led me to here. I now explore how my “arrow pushing” intuition stands up to a computational examination.
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Tags: anti-aromatic, ketene, lower energy pathways, pericyclic, Tutorial material
Posted in Curly arrows | 1 Comment »
November 13th, 2011
Following on from Armstrong’s almost electronic theory of chemistry in 1887-1890, and Beckmann’s radical idea around the same time that molecules undergoing transformations might do so via a reaction mechanism involving unseen intermediates (in his case, a transient enol of a ketone) I here describe how these concepts underwent further evolution in the early 1920s. My focus is on Edith Hilda Usherwood, who was then a PhD student at Imperial College working under the supervision of Martha Whitely.1
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Tags: 200-300, by-product, Christopher Ingold, energy, free energy, Hilda Usherwood, Historical, Imperial College, Martha Whitely, microwave, polymerization, RSC Publishing, United Kingdom
Posted in Interesting chemistry | 2 Comments »
November 10th, 2011
Fascination with nano-objects, molecules which resemble every day devices, is increasing. Thus the world’s smallest car has just been built[1]. The mechanics of such a device can often be understood in terms of chemical concepts taught to most students. So I thought I would have a go at this one!
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References
- T. Kudernac, N. Ruangsupapichat, M. Parschau, B. Maciá, N. Katsonis, S.R. Harutyunyan, K. Ernst, and B.L. Feringa, "Electrically driven directional motion of a four-wheeled molecule on a metal surface", Nature, vol. 479, pp. 208-211, 2011. https://doi.org/10.1038/nature10587
Tags: car drives, car rattling, chemical concepts, chemical name atropisomerism, chemical perspective, conformational analysis, day devices, energy, energy difference, Hubert Maehr, molecular car, nanocar, PDF, smallest car, Taxol
Posted in General, Interesting chemistry | 3 Comments »
November 7th, 2011
Henry Armstrong studied at the Royal College of Chemistry from 1865-7 and spent his subsequent career as an organic chemist at the Central College of the Imperial college of Science and technology until he retired in 1912. He spent the rest of his long life railing against the state of modern chemistry, saving much of his vitriol against (inter alia) the absurdity of ions, electronic theory in chemistry, quantum mechanics and nuclear bombardment in physics. He snarled at Robinson’s and Ingold’s new invention (ca 1926-1930) of electronic arrow pushing with the put down “bent arrows never hit their marks“.‡ He was dismissed as an “old fogy, stuck in a time warp about 1894.”‡ So why on earth would I want to write about him? Read on…
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Tags: Central College, electronic accounting, Henry Armstrong, Historical, Imperial College, Imperial college of Science and technology, New York, organic chemist, professor, Royal College of Chemistry, RSC Publishing, scientist, Stoney, Thomson, United States
Posted in Historical | 3 Comments »