Kathleen Lonsdale

Kathleen Lonsdale was an Irish-born crystallographer who used X-ray diffraction to settle a long-standing question in structural chemistry about the true shape of the benzene ring, a six-carbon molecular structure that is one of the most important building blocks in organic chemistry. In 1929, analyzing X-ray diffraction data from crystals of hexamethylbenzene, Lonsdale demonstrated conclusively that the benzene ring is a flat, hexagonal structure with all six carbon atoms lying in a single plane, resolving a debate among chemists that had continued since the ring structure was first proposed decades earlier. Lonsdale went on to a long career in X-ray crystallography, carrying out further important structural studies and also investigating the properties of diamond, work later commemorated when a rare form of meteoritic diamond was named lonsdaleite in her honor. In 1945 Lonsdale and biochemist Marjory Stephenson became the first two women ever elected as Fellows of the Royal Society, in its history since 1660, and Lonsdale later became the first female tenured professor at University College London as well as the first woman to serve as president of both the International Union of Crystallography and the British Association for the Advancement of Science; she was also a lifelong pacifist and advocate for prison reform, having herself served a prison sentence during the Second World War as a conscientious objector.