Using a combination of heat and light, symmetric σ-bonds can be broken asymmetrically, German researchers show in Nature.

The way chemical bonds break is fairly well understood. The valence bond theory, for example, says that the electrons in symmetric σ-bonds cannot split asymmetrically. But sometimes chemists want to bend the rules. For example, Anna Tiefel and colleagues at the University of Regensburg have succeeded in breaking symmetric Se-Se bonds ‘unfairly’.