Otto Wallach (27 March 1847 - 26 February 1931) was a German chemist and recipient of the 1910 Nobel prize in Chemistry for his work on alicyclic compounds.
Wallach was born in Königsberg, the son of a Prussian official. His father was transferred to Stettin (Szczecin) and later to Potsdam. Otto Wallach went to school, a Gymnasium, in Potsdam, where he learned about literature and the history of art, two subjects he was interested his whole life. At this time he also started private chemical experiments at the house of his parents.
In 1867 he started studying chemistry at the University of Göttingen, where at this time Friedrich Wöhler was head of organic chemistry. After one semester at the University of Berlin with August Wilhelm von Hofmann, Wallach received his Doctoral degree from the University of Göttingen in 1869, and worked as a Professor in the University of Bonn (1870-89) and the University of Göttingen (1889-1915). Wallach died at Göttingen.
During his work with Friedrich Kekulé in Bonn he started a systematic analysis of the terpenes present in essential oils. Up to this time only a few were isolated in pure form, and structural information was sparse. Melting point comparison and the measurement of mixtures was one of the methods to confirm identical substances. For this method the mostly liquid terpenes had to be transformed into crystalline compounds. With stepwise derivatisation, especially additions to the double bond present in some of the terpenes, he achieved the goal of obtaining crystalline compounds. The investigation of the rearrangement reactions of cyclic unsaturated terpenes made it possible to obtain the structure of a unknown terpene by following the rearangments to a known structure of a terpene. With these principal methods he opened the path to systematic research on terpenes.
He was responsible for naming terpene and pinene, and for undertaking the first systematic study of pinene^ . He also proposed that terpenes can be regarded as oligomers of isoprene; this is now known as the isoprene rule, and it assisted in the elucidation of the structures of many terpenes.
He wrote a book about the chemistry of terpenes, "Terpene und Campher" (1909).
He is also known for "Wallach's rule", that racemic crystals tend to be denser than their chiral counterparts. (Wallach, O. (1895). Liebigs Ann. Chem. 286, 90-143.). This rule has been substantiated by crystallographic database analysis (Brock et al., 1991).
* Leopold Ruzicka (1932). "Third Pedler lecture. The life and work of Otto Wallach". J. Chem. Soc.: 1582. doi:10.1039/JR9320001582.
* Carolyn Pratt Brock, W. Bernd Schweizer, and Jack D. Dunitz (1991). "On the validity of Wallach's rule: on the density and stability of racemic crystals compared with their chiral counterparts". J. Am. Chem. Soc. 113 (26): 9811. doi:10.1021/ja00026a015. http://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/ja00026a015.
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