The German Genius

Here are some modern structural formulae, where “R” equals “radical,” the simplest of which is “methyl”:

     

     
    The man who did more than anyone else to explain the operating principles of organic chemistry was August Kekulé. However, the circumstances of his various “discoveries” were controversial, and even after all this time they still divide historians of science.
    He was born on September 7, 1829, in Darmstadt, where von Liebig had been born a generation earlier; Kekulé sounds and looks as if it is French, but in fact the family was originally Bohemian nobility. 17 August studied architecture at Giessen, but fell under von Liebig’s spell and switched to chemistry. Later he argued that his architectural training (such as it was) had helped him to think in pictures—and this played a vital role when he came to identify the structure of carbon compounds.
    In 1854 he visited London and there, one summer evening, he made the first of his controversial claims. He said he had an important dream. These dreams aroused suspicion because, by their very nature, they could not be corroborated, and other scientists suspected Kekulé invented them to establish his own priority in his various claims to have identified the structure of organic substances. To give some idea of the controversy aroused, Archibald Scott Couper had written his first paper on organic bonds in 1858. Kekulé, however, said he had his dream about the same phenomenon in 1854 but didn’t say so until 1890.
    Organic chemistry may have had a difficult birth, but once the nature of the benzene ring was understood, the relatives of benzene—naphthalene, toluene, phenol (carbolic acid), cresols—soon became available on a vast scale, extracted from coal tar, producing a vast range of wealth-generating products: aniline dyes, trinitrotoluene, carbolic soap, creosote, naphthalene mothballs—the list is impressively long. The dyestuff industry led the way but “aromatic chemistry,” a term coined by Kekulé, proliferated over the following decades, producing endless industrial chemicals, but also powerful drugs like aspirin in 1899 and Paul Ehrlich’s pioneering antisyphilitic drug Salvarsan in 1909 (see Chapters 18 and 20). 18
    Benzene was at the center of this activity. Its formula, eventually understood as C 6 H 6 , was so stable that it could be transformed into many derivatives by substitution reactions without itself decomposing. Kekulé said that the structure of benzene came to him in yet another dream, this time in the winter of 1861–62, in Ghent. He said he dreamed of a snake that had seized hold of its own tail, leading Kekulé to publish his theory of the ring structure in 1865. (Arthur Koestler remarked dryly that this was “probably the most important dream in history since Joseph’s seven fat and seven lean cows.”)
    As John Buckingham has observed, “The benzene structure that emerged from the 1860s is a thing of considerable beauty and intellectual satisfaction…Like the DNA structure of nearly a century later, it had to be right.” 19 The ring is the key, meaning there are no reactive loose ends. Every carbon atom has two valencies that are used to bond it to its neighbors, while a third “hook” attaches it to a hydrogen atom. This leaves one over for a bond with something else. A complete understanding of benzene’s valency was not possible before the rise of quantum theory in the 1930s (see Chapter 32), but in the mid-nineteenth century chemists did begin to suspect that three-dimensional geometry might play a role in chemical reactions. This realization would help give rise to particle physics at the end of the nineteenth century, confirming Thomas Nipperdey’s point that the revolution in the natural sciences in the nineteenth century had a more far-reaching impact than the revolution brought about by Kepler, Galileo, and Newton.
    This new theoretical understanding had extremely practical consequences, accounting for the heroic developments in commercial chemistry after the 1860s, which helped Germany become a world economic—and then military—power. In 1862, in a letter to von Liebig, Wöhler worried at the large array of chemists being produced by German universities and queried their fate. 20 Only three years later, when Hermann Kolbe was appointed professor of chemistry at the University of Leipzig, he asked for—and was granted permission to build—a laboratory for 132 students. Von