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Interfering for the good
of a chemical reaction
Stuart A. Rice
Chemistry has, throughout its history, been a science of passive control: having made the conditions as favourable as possible, the chemist is obliged to let the complex reorganization of reactant molecules into products take place unhindered. But what if one could meddle at the very heart of a reaction to affect the dynamics of molecular evolution? Welcome to the world of quantum interference control.
The use of chemistry to support human activity is very old. Think of an archaeo-logical dig, and one immediately thinks
of pottery fragments, nails, ancient coins, perhaps metal-tipped weapons or tools ample evidence that exploitation of chemical operations preceded written history. In the earliest known written records, too, we find references to the preparation of fermented products such as wine and vinegar, and to dyeing and glass-making. It is clear that even in antiquity the amount of practical knowledge concerning chemical processes must have been considerable.
Of course, the relationships between different chemical processes were not yet recognized and organized, and the available knowledge could be transmitted only as practical rules of procedure. But the revolutionary idea that a particular substance can be converted into other substances by heating, dissolving or mixing must have spurred the search for new methods to control that transformation and steer it towards the desired products. The science of chemistry developed around that search, and its future will certainly include methods of reaction control unlike anything our forerunners could have imagined.
Over the past two centuries, chemistry has been set on a logical footing; intensive studies of synthetic methodology have given us many ways of generating a vast range of chemical species. The methods that are in current use rely on two fundamental procedures, or a combination of them. The first is the adjustment of a concentration ratio, either of reactants or intermediate species, so as to amplify the yield of the desired product. The second involves adjusting the rates of competing reactions that form different species from the same reactant (or intermediate) so as to enhance the formation of the one that is wanted. In practice, both methods are implemented by altering parameters such as the temperature, pressure, acidity or
solvent composition....