Christopher Kelk Ingold

Sir Christopher Kelk Ingold (October 28 1893 - December 8 1970, Edgware) was a British chemist based in Leeds and London. His groundbreaking work in the 1920s and 1930s on reaction mechanisms and the electronic structure of organic compounds was responsible for the introduction into mainstream chemistry of concepts like a nucleophile, electrophile, inductive and resonance effects, and such symbols as SN1, SN2, E1, E2. He also a co-author of the Cahn Ingold Prelog priority rules. He collaborated with his wife and fellow chemist E. Hilda Usherwood Ingold.

During his study of alkyl halides, Ingold found evidence for two possible reaction mechanisms for nucleophilic substitution reactions. He found that most secondary and tertiary alkyl halides underwent a two-step mechanism (SN1) while most primary alkyl halides underwent a one-step mechanism (SN2). This conclusion was based on the finding that reactions of most secondary and tertiary alkyl halides with nucleophiles were dependent on the concentration of the alkyl halide only. Meanwhile he discovered that primary alkyl halides, when reacting with nucleophiles, depend on both the concentration of the alkyl halide and the concentration of the nucleophile.

Sir Christopher received the Longstaff Medal of the Royal Society of Chemistry in 1951, the Royal Medal of the Royal Society in 1952, and was knighted in 1958. He began his scientific studies at Hartley University College at Southampton (now Southampton University) in 1913, obtaining his D.Sc at Imperial College, London in 1921. Following six years as Professor of Organic Chemistry at Leeds University, Ingold moved to University College London in 1930, where he was Head of the Chemistry Department from 1937 until his retirement in 1961. The department is today housed in the Sir Christopher Ingold laboratory, opened in 1969.