Nuclear magnetic resonance (NMR) allows us to detect atomic nuclei and say what sort of environment they are in within the molecule. In a molecule such as propanol, the hydrogen atom of the hydroxyl group is clearly different from the hydrogen atoms of its carbon skeleton—it can be displaced by sodium metal, for example. NMR (actually 1H, or proton, NMR) can easily distinguish between these two sorts of hydrogens by detecting the environ ment the hydrogen’s nucleus finds itself in. Moreover, it can also distinguish between all the other different sorts of hydrogen atoms present. Likewise, carbon (more precisely 13C) NMR can easily distinguish between the three different carbon atoms. NMR is extremely versatile: it can even scan living human brains (see picture) but the principle is still the same: being able to detect nuclei (and hence atoms) in different environments.