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MARGINALIA

Why Think Up New Molecules?

Adding to the world of known chemical structures is a wonderful mental experiment

Roald Hoffmann


Help, Where It is Needed

The universe is teeming with extreme conditions, from the interior of a big planet to the cold and near-vacuum surrounding a grain in an interstellar cloud. In the course of a chemical reaction, a number of molecular "intermediates" may have only the most fleeting of existences. Their properties, their very existence, may simply not be measurable—out there, or in the confines of the laboratory.

carbon-The%20carbon-based%20molecule%20cyclopropenylideneClick to Enlarge Image Here theoretical chemistry may really be of help. Quantum mechanics has already proved sufficiently reliable to calculate correctly the spectroscopic signatures of molecules in interstellar space. This is how a molecule relatively abundant out there, but hardly persistent in the laboratory, cyclopropenylidene, was detected (see the fourth figure, left) .

So it is for the metastable intermediates of chemical reactions. There is every reason to think that calculations of their properties are as easy (or is it "as difficult"?) as the properties of stable molecules.


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