CARBON, the element that is essential to all life, has sprung a baffling
surprise on chemists. An analysis of the 7 million or so known organic compounds
has shown that a significantly higher proportion contain even numbers of carbon
atoms than odd numbers. Yet carbon chemistry is so diverse that the number of
compounds with odd and even numbers should be roughly equal.
鈥淲e found this completely by accident,鈥� says Gautam Desiraju, professor of
chemistry at the University of Hyderabad in India. Desiraju was studying the
phenomenon of crystal polymorphism, in which individual organic compounds adopt
a variety of crystal structures. While he was screening a database of 150 000
carbon-based crystal structures, he realised that it contained about 15 per cent
more compounds with an even number of carbons than odd. 鈥淚 realised this was
something serious,鈥� he says.鈥�
When Desiraju told Jack Dunitz of the Swiss Federal Institute of Technology
in Zurich, the pair decided to broaden the investigation. Dunitz discovered that
the even-number compounds also dominate the world鈥檚 largest database of organic
compounds stored at the Beilstein Institute in Frankfurt.
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The researchers report their findings in this week鈥檚 Nature(vol 384,
p 320), but make no attempt to explain them. 鈥淚t鈥檚 much more intriguing if you
don鈥檛 offer an explanation,鈥� says Dunitz.