Archive for April, 2012

The Dieneone-phenol controversies.

Monday, April 30th, 2012

During the 1960s, a holy grail of synthetic chemists was to devise an efficient route to steroids. R. B. Woodward was one the chemists who undertook this challenge, starting from compounds known as dienones (e.g. 1) and their mysterious conversion to phenols (e.g. 2 or 3) under acidic conditions. This was also the golden era of mechanistic exploration, which coupled with an abundance of radioactive isotopes from the war effort had ignited the great dienone-phenol debates of that time (now largely forgotten). In a classic recording from the late 1970s, Woodward muses how chemistry had changed since he started in the early 1940s. In particular he notes how crystallography had revolutionised the reliability and speed of molecular structure determination. Here I speculate what he might have made of modern computational chemistry, and in particular whether it might cast new light on those mechanistic controversies of the past.

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Stereoselectivities of Proline-Catalyzed Asymmetric Intermolecular Aldol Reactions.

Sunday, April 22nd, 2012

Astronomers who discover an asteroid get to name it, mathematicians have theorems named after them. Synthetic chemists get to name molecules (Hector’s base and Meldrum’s acid spring to mind) and reactions between them. What do computational chemists get to name? Transition states! One of the most famous of recent years is the Houk-List.

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Perbromate. A riddle, wrapped in a mystery, inside an enigma; but perhaps there is a key.

Friday, April 6th, 2012

Chemists love a mystery as much as anyone. And gaps in patterns can be mysterious. Mendeleev’s period table had famous gaps which led to new discovery. And so from the 1890s onwards, chemists searched for the perbromate anion, BrO4. It represented a gap between perchlorate and periodate, both of which had long been known. As the failure to turn up perbromate persisted, the riddle deepened. Finally, in 1968, the key was found, but talk about sledgehammer to crack a nut! It was done by alchemical-like radioactive transmutation of selenium into bromine:

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A golden age for (computational) spectroscopy.

Monday, April 2nd, 2012

I mentioned in my last post an unjustly neglected paper from that golden age of 1951-1953 by Kirkwood and co. They had shown that Fischer’s famous guess for the absolute configurations of organic chiral molecules was correct. The two molecules used to infer this are shown below.

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