Benzene: The Dream of Kekule:

Continuing the subject of dreams, it is pertinent to mention that lucid dreams had helped many to make great discoveries and inventions. Since my subject is chemistry, I will touch upon one such famous dream which laid the foundation for understanding the structure and chemistry of  aromatic compounds.

As every one versed with chemistry knows, the benzene is the starting compound of aromatic compounds. Its structure was derived by Kukule’. His full name was Friedrich August Kekulé von Stradonitz.

Benzene was analyzed to have 6 carbon and 6 hydrogen atoms. Existing formula of all the organic compounds did not fit into the structure of benzene and explain its strange properties.

Kukule’ was working on this problem but could not find its solution. Totally engrossed, he fell into a sleep in front of fireplace. He has a dream of the atoms which he described in his own words as follows:

“...I was sitting writing on 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 gamboling 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 structures of manifold conformation; long rows sometimes more closely fitted together all twining and twisting in snake-like 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; and this time also I spent the rest of the night in working out the consequences of the hypothesis.”

So the snake he saw holding its own tail in its mouth was the the circular structure or closed ring structure of benzene. He immediately woke up and worked out his dream on the paper and by morning he had discovered the chemical structure of benzene.

From the chemical point, the formula of benzene is C₆H₆. Kekule proposed the following structure to explain the number of substitution compounds which have been synthesized  using this structure.

Still there were problems in explaining the two different compounds obtained when hydrogen atoms on adjacent carbons were substituted with two different radicals like Chloride, Nitrate, Iodide or C_xH_y. This is called ortho disubstituion. That is to say that C₆H₄XY will form two different ortho isomers depending  on whethere substitution has taken place C-C bond or C=C bond.  But such isomers have never been found. Kekule tried to explain this by saying that single and double bonds oscillate and thus become identical. Dr. Linus Pauling later on proposed resonance phenomenon, in which there are no purely single and double bonds but something in between and thus all C-C bonds are equivalent.

This has been conformed by UV analysis which shows all C-C bonds of equal strength and indistinguishable. This is like the Hindu God Shiva when He assumed ardhnarishwar or androgynous form to show that both male and female forms coexist in the body. The final outcome depends upon which of these dominate at a given time.

In the end of a lecture explaining the discovery of benzene, he said

“Let us learn to dream!”