pierre laszlo

language as an analogy in the natural sciences
Article Index
language as an analogy in the natural sciences
The elucidation of molecular structure
Building a molecule
Mixing and combining
The lesson from science history
Combinatorial chemistry
Parallels with linguistics
All Pages

2. Building a molecule

The complementary standard activity of chemists is synthesis. We make molecules. We build both natural substances and artificial products. There are many reasons and many aspects to such synthetic endeavor. Chemistry is both a science and an industry. Advancement of knowledge demands that we devise all sorts of new and crazy structures, molecules in the shape of knots, molecules in the shape of the Platonic solids, molecules in the shape of dendrimers or footballs, etc. The pharmaceutical industry has a voracious need for synthesizing rare but biologically active natural products as antitumorals, antihypertensors, antiretrovirals, insect antifeedants, etc. As a rule, such molecules stem from plants and they desport complex and delicate architectures, demanding exquisite skill in their step-by-step construction. Not only do we need to duplicate the natural construct, in order to make it abundant, we also synthesize hundreds of variants in order to try and improve potency as a drug while reducing undesirable side effects.

There is no need to elaborate further here about the need for synthesis. let me only say that the activity, like that of structural analysis, occupies the core of chemical science. The everyday practice of chemists in performing the multi-stage synthesis of a complex molecule assembles parts or modules, near-identical to those involved in (and identified by) the structural determination.

This buildup process is akin to word and sentence construction from the units of speech.

Historical reminder

The ethanol molecule (alcohol) had its elemental composition established early in the XIXth century. It was shown as equivalent to the sum of an ethylene molecule and a water molecule. And indeed, it proved feasible soon thereafter to synthesize ethanol by adding water to ethylene. This continues also to be one of its industrial preparations.

However, from the standpoint of chemical thought, equating for synthesis' sake a molecule to the sum of another two stable, existing molecules is sterile. Productive, fruitful thought does not consider ethanol as C2H6O = C2H4 + H2O, but as C2H5OH, i.e. as the union of the two radicals ethyl C2H5 and hydroxy OH. Why is it productive? Because these two units alone account also for other molecules, (C2H5)2 (butane) and (OH)2 (hydrogen peroxide).