When the Snake Bites its Own Tail

 

Carbon is a fairly social atom. It forms 4 links with other atoms to make up molecules. By comparison, oxygen looks a bit shy with only 2 links. And hydrogen is like introvert bordering on antisocial. Only one link!

These three atoms form some of the most useful and common molecules. Water is H₂O. We can show the 2 links between atoms by writing it like this: H-O-H. Similarly, carbon dioxide or CO₂ is in fact O=C=O. Carbon has 4 links, the oxygens have 2 links each, no worries.

Carbon and hydrogen compounds are called alkanes. The simplest is natural gas or methane, CH₄. Propane has a a chain of 3 carbon atoms. It is C₃H₈. Petrol is mostly octane with a chain of 8 carbon atoms, C₈H₁₈. Generally speaking, for a chain of n carbon atoms C, we need twice that number of H, plus one at each end. That is 2 x n + 2. Simple enough?

Enter the benzene. 

Back in 1865, August Kekule scratched his head on this one. With 6 carbon atoms, it should be C₆H₁₄ right? Wrong. The study of molecular mass shows C₆H₆. How can that be? Screw this, August said, I am going to have a nap. And he had a dream of a snake biting its own tail. He woke up and said aha! What if the carbon chain is a circle, or better a hexagon? Again everyone is stable and happy. It’s amazing how sometimes intuition and dreams can help science.