Dreams leading to discoveries- I find this subject very intriguing and I happen to bring this up with my students often to inspire them. I recently had one of my students ask, “Ma’am, do you remember Kekulé?” And that’s the inspiration behind this piece.
Have you heard of Benzene? Well, one might find it amusing that it took a dream of a snake biting its own tail, eventually leading to the revelation of the true structure of the benzene ring.
Benzene is a natural constituent of crude oil and one of the elementary petrochemicals having a wide range of applications. This colourless sweet smelling liquid is highly inflammable and is known to be an occupational carcinogen. The aroma of this molecule gives a characteristic smell to gasoline(petrol). Benzene is used for the manufacture of tons of other organic molecules which are industrially important. It is an important raw material in manufacturing plastics, resins, synthetic fibers, rubber lubricants, dyes, phenol, explosives, detergents, drugs, pesticides and therapeutic chemicals.
The origin of this hydrocarbon has a good old history. It was first isolated and identified by Michael Faraday in 1825 (Faraday is one of the greatest scientists the world has ever seen, who excelled both, in physics, and chemistry).
Molecular formula of benzene was deduced as C6H6. Each carbon has one hydrogen only. This means that the molecule is highly unsaturated. So determination of the structure of benzene was a mystery and real challenge for the scientists. Many structures were proposed, but none could explain the actual properties of the molecule (the molecule was poly unsaturated, but was extraordinarily stable, it was so stubborn)!
Later in 1865, the German chemist, Friedrich August Kekulé, published the structure of benzene, which explained all mulishness of the molecule. He gave a dynamic structural formula for benzene, a ring of 6 carbon atoms with alternate single and double bonds. It forms the basis for the modern electronic structure. This new understanding was proved to be a very important milestone in the development of organic chemistry.
The structure proposed was like this:
Later in 1890, in his speech during the silver jubilee celebrations of his benzene paper, Kekulé talked about the discovery of benzene structure.
In his words-
“I was sitting writing at my textbook, but the work did not progress; my thoughts were elsewhere. I turned my chair to the fire, and dozed. Again the atoms were gambolling before my eyes. This time the smaller groups kept modestly in the background. My mental eye, rendered more acute by the repeated visions of the kind, could now distinguish larger sections of manifold conformations: long rows, sometimes more closely fitted together; all twisting and turning in a snakelike motion. But look! What was that? One of the snakes had seized hold of its own tail, and the form whirled mockingly before my eyes. As if by a flash of lightning I awoke….I spent the rest of the night in working out the consequences of the hypothesis. Let us learn to dream gentlemen, and perhaps, we shall learn the truth.”
Inspite of many lampooneries over it, the Kekulé structure transcended time, and was confirmed crystallographically in 1929 by Dame Kathleen Lonsdale. We use the same hexagon with a waist band now also and it forms the basic unit in lakhs of organic molecules!