As hinted by the example (4112 → fluoxetine aka Prozac), look up the numbers in the Merck Index (12th ed.) They all reference either single elements or 1:1 compounds of two distinct elements.
Take the atomic number of each element and index into the alphabet. Random anagramming gives the answer FREQUENCY.
808 | Argon | Ar | 18 | R |
1345 | Boron | B | 5 | E |
1345 | Boron | B | 5 | E |
5405 | Lithium Chloride | Li/Cl | 3/17 | CQ |
5604 | Manganese | Mn | 25 | Y |
8348 | Scandium | Sc | 21 | U |
8439 | Silicon Carbide | Si/C | 14/6 | NF |