First new form of isomerism discovered in 50 years will be the last

Almost 170 years after Louis Pasteur discovered chirality by picking apart left- and right-handed tartaric acid crystals under the microscope, an entirely new form of stereoisomerism has been found in porphyrin–boron complexes. These isomers, based on hindered bond angle inversion, could make for unconventional drugs or find use in molecular computers. They are the last kind of isomer that will ever be discovered, according to the chemists behind the work.

The 1960s spelled another good decade for isomerism: in 1961, chemists realised they could make molecules with chiral phosphorus centres. Nitrogen-centred chirality followed in 1969. Usually nitrogen compounds undergo pyramidal inversion, akin to an umbrella flipping inside out. This process is extremely fast, which makes it impossible to separate the enantiomers. By confining the nitrogen within a three-membered heterocycle, chemists managed to make the first isolable aziridine enantiomers.