August Kekulé (1829-1896), a German professor of chemistry, had the most important dreams since the Bible: they led to scientific breakthroughs! They allowed him to work out how atoms go together to make different molecules – chemical structure. From that we know how to make chemicals, even stuff not found in nature, like plastic.
His family sent him to university to become an architect. But there he fell in love with chemistry instead. His parents were against it – there was no money in chemistry in those days – but he did not care.
Dream #1: The Dancing Atoms
One night in London on a late bus home Kekule fell asleep and dreamed of dancing atoms. At first they danced by themselves but then they joined hands and made pairs and then chains. The bigger atoms had more hands than smaller ones.
From this he got the idea that carbon atoms can bond with four other atoms and can form chains.
In the early 1800s scientists had worked out the chemical formulas for many substances. They found out, for example, that the alcohol in beer is made up of molecules that have two carbon atoms, six hydrogens and one oxygen:
But chemical formulas only told you how many atoms of each kind there were. It told you nothing about chemical structure, about how they went together.
The key was to know each chemical element’s valence: how many other atoms it could bond with.
As Kekule discovered, carbon had a valence of four. Oxygen had a valence of two and hydrogen, one.
Knowing that you can fit together the atoms of an alcohol molecule like so:
Or, in ball-and-stick form:
From structures like these it became clear how different chemicals could be put together – or taken apart – to form other chemicals.
These sort of structures worked well for most substances being studied at the time but not for benzene:
Dream #2: The Snake
Benzene has six atoms of carbon and six of hydrogen. According to Kekule’s ideas that was impossible. And yet benzene was real.
For years and years Kekule studied carbon-based chemistry (organic chemistry) but no luck. And then one night he fell asleep in front of his fireplace and had a dream.
He dreamed of snakes, long rows of them, moving and twisting. Then one of the snakes took hold of his tail to make a circle!
That was it: benzene was based not on a straight chain of carbon atoms but on a circle of six:
Notice the double bonds between some of the carbon atoms.
Because it is such a common chemical structure, it is now written like this for short:
Kekule did not live long enough to win a Nobel Prize in Chemistry, but his students won three of the first five: Jacobus van ‘t Hoff (1901), Hermann Fischer (1902) and Adolf von Baeyer (1905). Van ‘t Hoff added the idea of 3-D chemical structures. Von Baeyer used Kekule’s ideas to make indigo (the blue dye in blue jeans).