Adolf Karl Ludwig Claus (6 June 1838 – 4 May 1900) was a German

chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe th ...

. He is known for his structure of

benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...

proposed in 1867.

Life

Claus was born in 1838 in

Kassel Kassel (; in Germany, spelled Cassel until 1926) is a city on the Fulda River in northern Hesse, Germany. It is the administrative seat of the Regierungsbezirk Kassel and the district of the same name and had 201,048 inhabitants in December 2020 ...

, Germany. Starting from 1850, he studied medicine in Marburg and later chemistry at the

University of Marburg The Philipps University of Marburg (german: Philipps-Universität Marburg) was founded in 1527 by Philip I, Landgrave of Hesse, which makes it one of Germany's oldest universities and the oldest still operating Protestant university in the wor ...

, with

Hermann Kolbe Adolph Wilhelm Hermann Kolbe (27 September 1818 – 25 November 1884) was a major contributor to the birth of modern organic chemistry. He was a professor at Marburg and Leipzig. Kolbe was the first to apply the term synthesis in a chemical cont ...

. After spending a short time at the

University of Berlin Humboldt-Universität zu Berlin (german: Humboldt-Universität zu Berlin, abbreviated HU Berlin) is a German public research university in the central borough of Mitte in Berlin. It was established by Frederick William III on the initiative o ...

, he worked with

Friedrich Wöhler Friedrich Wöhler () FRS(For) HonFRSE (31 July 180023 September 1882) was a German chemist known for his work in inorganic chemistry, being the first to isolate the chemical elements beryllium and yttrium in pure metallic form. He was the firs ...

at the

University of Göttingen The University of Göttingen, officially the Georg August University of Göttingen, (german: Georg-August-Universität Göttingen, known informally as Georgia Augusta) is a public research university in the city of Göttingen, Germany. Founded ...

. He received his PhD in 1862, and in the same year changed his position and started working at the

University of Freiburg The University of Freiburg (colloquially german: Uni Freiburg), officially the Albert Ludwig University of Freiburg (german: Albert-Ludwigs-Universität Freiburg), is a public university, public research university located in Freiburg im Breisg ...

. He completed his

habilitation Habilitation is the highest university degree, or the procedure by which it is achieved, in many European countries. The candidate fulfills a university's set criteria of excellence in research, teaching and further education, usually including a ...

in 1866 and became assistant professor in the following year. With the retirement of

Lambert Heinrich von Babo Lambert Heinrich Joseph Anton Konrad Freiherr von Babo (November 25, 1818 – April 15, 1899) was a German chemist. Life Babo was the son of the agronomist Lambert Joseph von Babo and his first wife Karoline Ehrmann. The oenologist August Wilhe ...

, Claus succeeded him as full professor. He held that position until his retirement due to health problems in 1900. Clause died in Horheim near

Wutöschingen Wutöschingen is one of the 25 Municipality, municipalities in the Waldshut (district), Waldshut district (''Kreis'') of Baden-Württemberg, Germany. References

Waldshut (district) Baden {{Waldshut-geo-stub ...

in the same year.

Work

Claus mostly worked in organic chemistry where his interests were very diverse and included

alkaloid Alkaloids are a class of basic, naturally occurring organic compounds that contain at least one nitrogen atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar ...

s, aromatic substitution, oximes and theoretical considerations on the structure of organic molecules. Claus is best known for proposing a model of

molecule in 1867. In his model, the six carbon atoms of benzene form a hexagon with a hydrogen atom attached to every corner. To preserve valence 4 for carbons, the opposite corners of the hexagon are connected by single bonds. It took years of research before the three postulated structures of benzene – by

Albert Ladenburg Albert Ladenburg (July 2, 1842August 15, 1911) was a German chemist. Early life and education Ladenburg was a member of the well-known Jewish in Mannheim. He was educated at a Realgymnasium at Mannheim and then, after the age of 15, at the tec ...

(1869),

August Kekulé Friedrich August Kekulé, later Friedrich August Kekule von Stradonitz ( , ; 7 September 1829 – 13 July 1896), was a German organic chemist. From the 1850s until his death, Kekulé was one of the most prominent chemists in Europe, especially ...

1865 and by Claus – found their place in organic chemistry. Ladenburg's

prismane Prismane or 'Ladenburg benzene' is a polycyclic hydrocarbon with the formula C6H6. It is an isomer of benzene, specifically a valence isomer. Prismane is far less stable than benzene. The carbon (and hydrogen) atoms of the prismane molecule are a ...

and

Claus' benzene Claus' benzene (C6H6) is a hypothetical hydrocarbon and an isomer of benzene. It was proposed by Adolf Karl Ludwig Claus in 1867 as a possible structure for benzene at a time when the structure of benzene was still being debated. The molecule can ...

were both proven to be wrong. While the prismane was synthesized in 1973, calculations showed that the synthesis of

is impossible. Claus synthesized and determined the structure of several

isomers In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. ...

oxime In organic chemistry, an oxime is a organic compound belonging to the imines, with the general formula , where R is an organic side-chain and R’ may be hydrogen, forming an aldoxime, or another organic group, forming a ketoxime. O-substituted ...

s. He described the isomerism by differences in the bond structure of the molecules whereas several other scientists found it more convincing to describe the difference by the relatively new concept of

stereochemistry Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereois ...

. This scientific dispute lasted until his death in 1900.

References

{{DEFAULTSORT:Claus, Adolf Karl Ludwig 1838 births 1900 deaths 19th-century German chemists