Kekulé, Friedrich August – The Origins of the Structural Theory
Type of Spiritual Experience
The new understanding of benzene, and hence of all aromatic compounds, proved to be so important for both pure and applied chemistry after 1865 that in 1890 the German Chemical Society organized an elaborate appreciation in Kekulé's honor, celebrating the twenty-fifth anniversary of his first benzene paper. Here Kekulé spoke of the creation of the theory.
He said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake seizing its own tail (this is a common ancient symbol known as the ouroboros). This vision, he said, came to him after years of studying the nature of carbon-carbon bonds. ....... He told yet another anecdote in 1890, of a vision of dancing atoms and molecules that led to his theory of structure. This happened, he claimed, while he was riding on the upper deck of a horse-drawn omnibus in London. If true, this probably occurred in the late summer of 1855.
A description of the experience
From a Speech made at the celebration in Berlin’s City Hall in 1890, celebrating the 25th anniversary of the formula for benzene
This speech was subsequently published in a major German chemistry journal and were translated into English in 1958
You are celebrating the jubilee of the benzene theory. I must first of all tell you that for me the benzene theory was only a consequence, and a very obvious consequence of the views that I had formed about the valences of the atoms and the nature of their binding, the views, therefore, which we now call valence and structural theory. What else could I have done with the unused valences?
During my stay in London I resided in Clapham Road....I frequently, however, spent my evenings with my friend Hugo Mueller....We talked of many things but most often of our beloved chemistry. One fine summer evening I was returning by the last bus, riding outside as usual, through the deserted streets of the city....I fell into a reverie, and lo, the atoms were gamboling before my eyes. Whenever, hitherto, these diminutive beings had appeared to me, they had always been in motion; but up to that time I had never been able to discern the nature of their motion. Now, however, I saw how, frequently, two smaller atoms united to form a pair: how a larger one embraced the two smaller ones; how still larger ones kept hold of three or even four of the smaller: whilstthe whole kept whirling in a giddy dance. I saw how the larger ones formed a chain, dragging the smaller ones after them but only at the ends of the chains....The cry of the conductor: "Clapham Road," awakened me from my dreaming; but I spent a part of the night in putting on paper at least sketches of these dream forms. This was the origin of the "Structural Theory”.