The search for the grand unification of aromaticity
Researchers have been trying to find a full definition of aromaticity for almost two centuries, and yet keep discovering new types
‘Controversial’, ‘suspicious’, ‘questionable’ and even ‘an exercise in chemical futility’ – these are only some of the ways scientists have described the concept of aromaticity. And that’s in spite of it being a concept that almost all chemists are familiar with from school or university.
PubChem, the largest public database of chemical compounds, contains almost 110 million structures. There’s an estimate that two-thirds of them are fully or partially aromatic. Understanding how aromaticity influences a compound’s properties allows researchers to design everything from drugs to molecular light emitters.
The problem with aromaticity is that, despite 200 years of research, there’s no clear definition, rules or experiments that can identify it among all compounds. Despite chemists having access to an ever-increasing number of shorthand rules and a vast array of computational methods, they keep finding aromaticity in unexpected places. But with more than 20 different types of aromaticity described so far, how close are chemists to finding a definition that unites all of them?