THIELE, F. K. JOHANNES

(b. Ratibor, Upper Silesia, Germany [now Reciborz, Poland], 13 May 1865; d. Strasbourg, Germany [now France], 17 April 1918)

chemistry.

Thiele, a major contributor to our knowledge of nitrogen compounds and to the theory of unsaturated organic molecules, was the second of six children of Friedrich August Thiele, a leading citizen of Ratibor and owner of a publishing house and bookstore. His mother, the former Elfriede Koppe, died when he was six. Thiele studied at the University of Breslau (1883–1884) and then at Halle under Jacob Volhard, obtained his doctorate there in 1890, and taught analytical and organic chemistry. His studies on the nitrogen compounds guanidine and hydrazine and their derivatives, some of them explosive, interested both industry and government.

In 1893 Thiele became associate professor under Adolf von Baeyer at Munich, where he continued his work on nitrogen derivatives and developed his most important research, which dealt with conjugated unsaturated systems–structures involving alternate single and double bonds along a chain of atoms. In 1902 he was appointed professor at Strasbourg, where he expanded and modernized the chemical institute and in 1910 became rector of the university. During World War I, Thiele served for a time as a censor of telegrams and developed a gas mask against carbon monoxide. On Volhard’s death in 1910, he became editor of Justus Liebig’s Annalen der Chemie. In the same year he was elected to the Munich Academy of Sciences. He died, unmarried, of a heart ailment at age fifty-three.

Organic chemistry seemed divided, in the latter nineteenth century, into two parts–the derivatives of benzene, C₆H₆, and the rest, including unsaturated compounds. The latter, containing double or triple bonds, and –C ≡ C–, added bromine (and other reagents) readily, forming and –CBr₂–CBr₂–. Benzene, to which Kekulé in 1865 had assigned a structure with three double bonds

was quite unreactive, however, adding bromine only in the presence of light.

Thiele constructed a bridge between the two realms. Building on Fittig’s and A. von Baeyer’s discovery that structures C═C—C═C added hydrogen, H₂, not as expected, at a double bond, but at the ends of the chain, thereby yielding CH—C═C–CH, with a new double bond in the center, Thiele proposed that “double bond” is a misnomer because the atoms are not bound twice as strongly as when singly bound. Rather, doubly bound carbon atoms retain a “partial valence” that explains their reactivity. In a system of alternating single and double bonds, which Thiele called a “conjugated system,” the inner partial valences neutralize each other, leaving the end atoms reactive.

Since benzene has a closed conjugated system

its lack of reactivity is explained.¹ Thiele’s theory stimulated extensive research by himself and others, and was a direct precursor of electronic thoeries of organic reaction mechanisms.²

Thiele’s extensive research on nitrogen chemistry, particularly on derivatives of hydrazine [H₂NNH₂], and guanidine [HN═C(NH₂)₂], led to the discovery of numerous new compounds and new synthetic processes. He prepared nitramide (NH₂NO₂), which is isomeric with hyponitrous acid (H₂N₂O₂); these were the first examples in inorganic chemistry of compounds having identical molecular formulas but different properties. He also achieved the synthesis of five- and sevenmembered ring compounds containing nitrogen.

NOTES

1. J. Thiele, “Zur Kenntnis der ungesättigten Verbindungen,” in Justus Liebig’s Annalen der Chemie,306 (1899), 87–266; 319 (1901), 129–143.

2. C. K. Ingold, Structure and Mechanism in Organic Chemistry, 2nd ed., p. 76.

BIBLIOGRAPHY

I. Original Works. A full bibliography, listing over 130 articles and the titles of dissertations by Thiele’s students, is included in the obituary by F. Straus (see below). A section of Thiele’s paper on conjugated systems (Annalen der Chemie,306 [1899], 89–90) is translated in H. M. Leicester and H. S. Klickstein, eds., A Sourcebook in Chemistry (New York, 1952), 510–511.

II. Secondary Literature. Fritz Straus, “Johannes Thiele,” in Berichte der Deutschen chemischen Gesellschaft,60 (1927), 75A–132A, consists of an obituary, extensive discussion of his chemical work, and full bibliography. Poggendorff, IV, 1489–1490, and V, 1249–1250, presents biographical notes and bibliography. J. R. Partington, A History of Chemistry,IV (London, 1964), 847–848, summarizes Thiele’s chemical contributions and includes important references. Thiele’s theory of partial valences is discussed in F. Henrich, Theorien der organischen Chemie (Brunswick, 1912), 34–82; in E. Hjelt, Geschichte der organischen Chemie (Brunswick, 1916), 459–460, 467–469; and, more recently, in C. K. Ingold, Structure and Mechanism in Organic Chemistry, 2nd ed. (Ithaca, N.Y., 1969), 75–77, 184, 957–958.

Thiele’s contributions to the chemistry of organic nitrogen compounds are referred to in N. V. Sidgwick, T.W.J.Taylor, and W. Baker, The Organic Chemistry of Nitrogen (Oxford, 1937), 274, 286, 297, 348, 361, 378, 384, 446.

Otto Theodor Benfey