Philip Ball delights in tortured carbon atoms

Are chemists sadists? An outsider, noticing their delight in the synthesis of molecules that are strained, distorted, bent and squeezed, might reasonably suspect so. In a recent essay, Roald Hoffmann of Cornell University in Ithaca, New York, US, and Henning Hopf of the Technical University of Braunschweig, Germany, explore the phenomenon. 

The usual answer is that scientists can learn about normality through extremes. Astrophysicists and high-energy physicists believe that to understand reality we must gaze into the most awesome furnaces. The approach is also common in philosophy, exemplified by the practice of reductio ad absurdum and by the idea that the exception proves (in the original sense of ‘tests’) the rule.  

These principles are evident in chemists’ explorations of the abnormal. By investigating how far a carbon vertex can be bent before it spontaneously flies apart, we gain some understanding of the parameters within which such frameworks must operate. It has been long recognised, for example, that the Platonic polyhedral alkanes stop at cubane, a cube; tetrahedrane is unstable, its tortured bonds angles too much to bear (even though a single face of the polyhedron, the triangular cyclopropane, is precariously stable).  

Chemists don’t give up that easily, however, and in 1978 Günther Maier and his colleagues at the University of Marburg, Germany, made a version of tetrahedrane with t-butyl (C(CH3)3) groups at the corners. The popular notion is that encasement in bulky groups provides a kind of corset that contains the strain energy, but I’m reliably informed that the stability of the molecule actually owes more to the buffering from collisions that would otherwise spring open the cage. 

As well as molecules having their arms twisted, they can also be put on the rack. For example, anthracene will photo-dimerise into a kind of four-bladed molecule with two unusually long bridging C-C bonds (1.618Å, compared with the normal 1.54Å), stretched by steric repulsion. 

Molecular deviance 

Hoffmann and Hopf are not content to accept such conventional explanations for chemists’ fascination with molecular deviance, and instead explore the scientists’ psychology. ‘We bet there would be less interest, less drive to actually make such molecules if the colloquial descriptors of a degree of molecular suffering were to be proscribed,’ they write. Indeed, chemistry is full of such terms - just think of attacking and protecting groups. 

Distorted molecules are a particularly interesting case, however, because here chemists consciously set out to make objects that are weird, deviant, perhaps even break the rules, and which arguably, once you have imbibed chemistry’s molecular aesthetics, are grotesque.  

Of course, a big part of the impulse to make any new molecule is the intellectual challenge, and the desire to be the first to do so. There is also an element of sheer playfulness, evident in the whimsical names for these molecules: basketane, pagodane, olympiadane. 

Cabinet of curiosities 

Does that, though, suffice to explain the fascination with what Hoffmann and Hopf call ‘unhappy molecules’? They don’t really see sadism afoot here, but argue that nevertheless there does seem to be a potential link to the broader narratives of the notorious Marquis.  

Chemist and writer Pierre Laszlo agrees: ‘the monstrous is a major theme of Sade. Western science is underlined by its sense of wonder. Monsters are and remain an integral part of it. Such seeking for the abnormal is blatant in chemistry.’ 

Monsters and mutants were abundant in the cabinets of curiosities kept by 17th century patrons of the sciences, and it was often by examining such objects that early developmental biologists began to glean clues about the genetics of embryogenesis. And if you think this all seems remote from chemistry, just look at the front and back pages of Cram and Hammond, the definitive textbook of organic chemistry.  

There you’ll find a cabinet of curiosities in the form of many strained, bent and otherwise peculiar hydrocarbons, either made already or laying down the gauntlet to the synthetic chemist - an invitation, you might say, to the connoisseurs of molecular deviance.