2-N-Imidazolyl- and 2-N-pyrazolyl-1,3-indandiones

It was shown by spectroscopic methods that 2-N-imidazolyl-, 2-N-(N-methylimidazolyl)-, and 2-N-(N-methylpyrazolyl)-1,3-indandiones exist in the form of inner salts, whereas 2-N-pyrazolyl-1,3-indandione exists in the form of an enol with an intramolecular hydrogen bond.