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By Saranja Sivachelvam
“It is a truth universally acknowledged, that a single molecule in possession of an interesting structure, must be in want of an image”. [David Fox]
UK chemists Anish Mistry and David Fox of the University of Warwick have thrown chemistry’s share into London 2012 with the synthesis of Olympicene, a molecule resembling the five interlocking rings that form the symbol of the Olympic Games. The symbol, consisting of five rings – blue, yellow, black, green, red – was originally designed by Baron Pierre de Coubertin, the founder of the modern Olympic Games in 1912, and represents the five regions of the world that compete in the Games.
Former head of department of Oxford Chemistry, Professor Graham Richards CBE, first came up with the brilliant idea of synthesising Olympicene to mark the highly anticipated London 2012 games. “I was in a committee meeting of the Royal Society of Chemistry (RSC) where we were trying to think of what we could do to mark the Olympics… it occurred to me that the molecule that I had drawn looked very much like the Olympic rings, and it had never been made.”
Olympicene is an aromatic molecule, containing eighteen pi electrons in its ring system, and is formed of four linked benzene rings joined by a –CH2- spacer. Its synthesis brings to mind some familiar reactions that the first year Oxford chemists covered last year, starting with the Wittig reaction of pyrene carboxaldehyde. The required ylid (a neutral dipolar molecule containing a formally negatively charged atom (usually a carbanion) directly attached to a heteroatom with a formal positive charge) was obtained by reacting triphenylphosphine with ethyl bromoacetate to form a phosphonium salt, which after treatment with a mild base, was reacted with the aldehyde in toluene. The resultant alpha,beta-unsaturated carbonyl compound was hydrogenated using hydrogen and palladium in ethyl acetate to give an ester, which was then reacted with potassium hydroxide, acid and thionyl chloride to give the acid chloride. The ketone was formed via the Friedel-Crafts reaction (aluminium chloride in dichloromethane), reduced using lithium aluminium hydride and treated with acid to give the final product.
Once the final product (2H-benzo[cd]pyrene) had been made, it was received by the UBM Research facility in Zurich, Switzerland for imaging using a carbon monoxide tipped atomic microscopy technique that allows the structure and bonding in a molecule to be seen.
But Olympicene was not just synthesised for aesthetic purposes – it has some useful properties too.
“Alongside the scientific challenge involved in creating olympicene in a laboratory, there’s some serious practical reasons for working with molecules like this,” said Dr Fox.
“The compound is related to single-layer graphite, also known as graphene, and is one of a number of related compounds which potentially have interesting electronic and optical properties… For example these types of molecules may offer great potential for the next generation of solar cells and high-tech lighting sources such as LEDs.”