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- George Andrew Olah, (born 1927), 1994 Nobel Prize in Chemistry
- Lars Onsager, (1903–1976), physical chemist, 1968 Nobel Prize in Chemistry
- Joan Oró, (1923–2004), Catalan biochemist, one of his most important contributions was the prebiotic synthesis of the nucleobase adenine from hydrogen cyanide.
- Hans Christian Ørsted, First to isolate aluminium
- Wilhelm Ostwald, (1853–1932), 1909 Nobel Prize in Chemistry
Read more about this topic: List Of Chemists