Read more: “Impossible reactions: Five chemistry rules broken“
A chemical bond is a union between two atoms. The idea that, on occasions, a third atom might hop into the bed was so offensive when it was first proposed that it provoked a decades-long flame war.
It all started in the 1940s, with attempts to explain certain reactions of organic molecules that involved the swapping of negatively charged dangling groups. If one such group fell off, that left the rest of the molecule as a “carbocation”, an ion containing a positively charged carbon atom. By rights the replacement group should have attached itself at the same place, at the positively charged atom. But it didn’t always.
Advertisement
Some chemists, in particular Saul Winstein of the University of California, Los Angeles, championed a startling explanation: that the positive charge was smeared between a triangular array of three carbon atoms in the carbocation. This “non-classical” bonding structure gave the replacement group more than one place to dock – and temporarily, and rather heretically, gave one of the carbon atoms five bonding partners instead of the usual four.
Herbert Brown, a US chemist who was for his work on boron compounds, was particularly incensed by this proposal. In 1961, he opened what he described as a “holy war”, dismissing the idea of the non-classical ions as lacking “the same care and same sound experimental basis … customary in other areas of experimental organic chemistry”.
In the absence of any cast-iron way to interpret the results of the experiments, the argument motored on for two decades, eventually sputtering to a halt only in the early 1980s. By that time, most chemists except Brown accepted that the non-classical bonds were real. As it turned out, neither side was radical enough: Winstein and Brown both suggested to a young Hungarian emigré chemist, George Olah, that his claim to have isolated a relatively long-lived carbocation was misguided. This was another “reaction that couldn’t happen”, they insisted, because carbocations were too unstable. Using nuclear magnetic resonance spectroscopy, however, Olah both proved that he was right and also supplied the best evidence that the three-atom non-classical bond does indeed exist. Olah’s work on carbocations eventually earned him a Nobel prize in 1994.
When this article was first posted, it incorrectly called Saul Winstein “Sam”.