Field of Science

One ring to bind them all: things you might not know about benzene

Space filling model.  c. Michelle Francl
UPDATE:  The Sceptical Chemist has a quiz up on benzene structural formulae based on the article in Nature Chemistry.  

Next year is the 150th anniversary of Kekulé's paper proposing the cyclic nature of the benzene 'nucleus.' and the 190th anniversary of Michael Faraday's paper on bi-carburet of hydrogen, more familiarly known as benzene.  In Berlin in 1890, on the 25th anniversary, German chemists threw the Benzolfest in honor of Kekulé.

I wrote a short 'fest' for Nature Chemistry, which appears in the January issue($).  I learned much about organic chemistry's iconic molecule, and herewith are 10 pieces of trivia that did not make it into the final piece.

1. There are 217 skeletal isomers of benzene, including the iconic hexagon, more than 300 if you count stereoisomers. [Patrick W. Fowler, MATCH Commun. Math. Comput. Chem. 63 (2010) 333-346].

 2. Benzene tastes sweet, with a hint of almond, and can be tasted in water starting at about 0.5 ppm, or roughly 1 drop in 40 gallons.

 3. An alternate synthesis (circa 1850) claims to passes benzoic acid through a “red hot gun” barrel packed with pumice. There's no evidence that it actually works.

 4. There is a tie knot that is hexagonal, perfect for tie-wearing chemistry conference attendees.  It was discovered by mathematicians, but you can still wear it.

 5. Dewar never suggested benzene's preferred structure was bicyclic. He used the structure, along with the more conventional structure, to demonstrate the potential of his brass molecular models. ["On the oxidation of phenyl alcohol, and a mechanical arrangement adapted to illustrate structure in the non-saturated hydrocarbons," Proceedings of the Royal Society of Edinburgh 6: 82–86 (1867), you can find it on Google Books]

6. The extraction of flowers of benzoin - benzoic acid - was first reported by Michel de Nostredame, otherwise known as Nostradamus, in the 16th century.

7  Kekulé actually didn't didn't present his revolutionary theory in January of 1865, his colleague Adolphe Wurtz read the paper in his absence.

8.  As late as the 1920s, major figures in organic chemistry did not think benzene or its derivatives were planar.  Sixty four years after Kekulé's paper was submitted (almost to the day), crystallographer Kathleen Lonsdale submitted her paper showing unequivocally that hexamethyl benzene, and presumably therefore benzene, was planar. "Thus the 'diamond' [puckered] type of benzene ring is shown to be wholly inadmissible." (Emphasis is Lonsdale's.) [K. Lonsdale, Proc. Roy. Soc. A, 494-515, 1929.]

9. In the days before ChemDraw, there were stamps.

10.  Hexagons were not the only proposed structural formula for benzene.  Loschmidt suggested the representation at the right.

If you would like a reprint of the essay, send me an email.

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