Christopher Kelk Ingold
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Sir Christopher Kelk Ingold (1893-1970) was a British chemist based in Leeds and London. He 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 2 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 1 step mechanism (SN2). This conclusion was based on the finding that reactions of most secondary and tertiary alkyl halides with nucleophiles were dependant 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.
