Organic chemistry textbooks will need to be revised to recognize a chemical species that chemists have discovered. The species - pentamethylcyclopentadienyl cation (a positively charged ion) - was thought not to exist for long because theory said it was unstable.
"I've said this molecule is unstable and doesn't exist dozens of times in organic chemistry class, but, as it turns out, the molecule had different ideas," said Joseph B. Lambert, Clare Hamilton Hall Professor of Chemistry at Northwestern. He and graduate student Lijun Lin discovered that the cation is stable in the solid state for weeks at room temperature and in solution.
The cyclopentadienyl cation is a common textbook example of an antiaromatic molecule, a molecule so electronically unstable and, therefore, extremely reactive that it should not exist for any length of time. Lambert believes the cation now should be described as nonaromatic.
Lambert and Lin discovered the molecule when trying to figure out how to make stable organic cations in the laboratory. When Lin came to Lambert with the crystal structure of a molecule other than the one expected, Lambert quickly recognized the structure as an example of the elusive cyclopentadienyl cation of textbook fame. Lambert and Lin currently are studying the chemistry of the pentamethylcyclopentadienyl cation by carrying out reactions with the cation to learn more about its properties.