Otto Paul Hermann Diels (; 23 January 1876 – 7 March 1954) was a
German chemist. His most notable work was done with
Kurt Alder on the
Diels–Alder reaction, a method for
diene synthesis. The pair was awarded the
Nobel Prize in Chemistry in 1950 for their work. Their method of synthesizing cyclic organic compounds proved valuable for the manufacture of synthetic rubber and plastic. He completed his education at the
University of Berlin, where he later worked. Diels was employed at the
University of Kiel when he completed his Nobel Prize–winning work, and remained there until he retired in 1945. Diels was married, with five children. He died in 1954.