New database unlocks predictive power of radical polarity

Researchers in the US have compiled a comprehensive catalogue of over 500 radicals – each classified by its electron-seeking or electron-donating tendencies, and summarised them in a helpful chart. The study stands out as the first large-scale quantification of radical polarity, a critical yet elusive property dictating reaction selectivity and efficiency.

Using a combination of advanced computational models and real-world experiments, David Nagib at Ohio State University and colleagues measured the impact of radical polarity on reaction selectivity. By testing reactions like hydrogen atom-transfer and π-additions with over 50 radicals, the team observed that even a slight polarity shift could yield drastic changes in reaction speed – sometimes up to a four-fold increase. These insights were validated through competition experiments that confirmed that radical polarities directly influence which reaction pathways are favoured. For example, electrophilic radicals excelled in anti-Markovnikov additions to electron-rich alkenes, while nucleophilic radicals were more selective in Giese additions to electron-deficient alkenes.

Despite providing valuable insights into radical-based reactions, the predictive power of the database can vary in complex, multi-step reactions where additional factors – including sterics, solvent effects or secondary interactions – could influence radical behaviour beyond polarity alone.