The German organic chemist Otto Paul Hermann Diels (1876-1954) discovered a technique of atomic combination which led to the synthesis of an important group of organic compounds.

Hermann Diels was born in Hamburg on Jan. 23, 1876. After studying chemistry at the University of Berlin he was awarded a doctoral degree in 1899. In that year he joined the faculty as assistant professor and became associate professor in 1914. He became professor of chemistry at the University of Kiel in 1916 and held this position until his retirement in 1948.

In his early work at Berlin, Diels discovered carbon suboxide (1906) and investigated its properties. The compound was important because of its high degree of reactivity and because its chemical structure provided important information as to the composition of other oxides of the carbon atom. However, Diels's most important work was done at Kiel, where he was assisted by Kurt Alder. Together they were able to work out the technique of a new atomic combination.

The now famous Diels-Alder reaction involved a diene synthesis. In this reaction there appeared a new molecular structure, one which hitherto had not been recognized. It consisted of what came to be identified as a conjugated diene, that is, an organic substance containing two double-bonded carbon atoms in a ring compound. The first experiments showed that the compound butadiene would react vigorously with maleic anhydride to produce a six-membered ring compound, and further experimentation showed that the simple dienes, such as butadiene, could be changed into cyclic dienes, which, in turn, could be used as the bases for a new group of organic compounds.

One of the most remarkable aspects of the Diels-Alder reaction was the lack of a need for reagents, catalysts, or high temperatures and pressures. The process proceeded at a relatively slow pace at temperatures usually associated with animal organisms. The potentiality of the reaction was profound. Diels went on to one synthesis after another, among the most notable being that of the polymerization of the diene isoprene into synthetic rubber. Other investigators produced a whole family of plastics, alkaloids, and polymers from the technique of the Diels-Alder reaction. The synthesis of cortisone was an outcome of this technique. In addition to this work, Diels also investigated cholesterol and bile acids, and the degradation products involved in dehydrogenation brought about by the use of the metal selenium.

Although the new organic products for which Diels was so much responsible may have produced benefits for mankind, it should not be forgotten that one of the most important parts of his research was a new insight into chemical combination and molecular structure. In 1950, in recognition of his many contributions to chemical science, Diels, together with Alder, was awarded the Nobel Prize. Diels died at Kiel on March 7, 1954.

Further Reading

• There is virtually nothing in English on the life of Diels. However, for discussions of his scientific achievements, the reader should consult Eduard Farber, Nobel Prize Winners in Chemistry, 1901-1961 (1953; rev. ed. 1963); Aaron J. Ihde, The Development of Modern Chemistry (1964); Nobel Foundation, Chemistry: Nobel Lectures, Including Presentation Speeches and Laureates' Biographies, vol. 3 (1964); and James R. Partington, A History of Chemistry, vol. 4 (1964).