1. The elucidation of molecular structure.
Chemistry is to a very large extent a molecular science. The first task in a laboratory is to determine the structure, viz. the arrangement of the atoms relative to one another, in a new molecule, whether natural or man-made. I won’t dwell on the technical aspects, mass spectrometry and nuclear magnetic resonance are the tools of choice for such structural determination. What these methodologies provide however is not a three-dimensional model of the molecule, showing the atoms with their actual positions. Such model building comes afterwards, almost as an afterthought and is not that important. The information that chemists need and obtain from such structural analysis is of an altogether different type. Let me make an analogy. If the molecular model were to be built from a Lego set, the pieces of Lego are identified, one by one, and handed to the chemist, in the correct sequence for building up the appropriate structure, as contrasted with one of the numerous isomers.
The Lego units or modules I am referring to are methyl groups CH3, hydroxy groups OH, phenyl groups C6H5, carbonyls CO, etc. They are the radicals that were introduced in the 1850s by Dumas, Laurent, Liebig, only after a heated controversy. These radicals had the beneficial effect of removing chemistry from the status of a natural science and to prop it up into what Popper would term World 3, i.e. to replace positivist chemical species with what, at that time of the mid-Nineteenth Century, were merely Platonic archetypes. But radicals, these idealized concepts, have been fantastically productive, and they continue to constitute the core of structural chemistry.
Hence, I beg you to trust me if I assert, to summarize this first observation of what chemists really do in their laboratories, that the everyday practice of chemists in elucidating the structure of an unknown compound produces semantic units, analogous to phonemes in language.