Summary The general properties of imidazoles are discussed, taking into consideration resonance and tautomerism. Comparisons with similar openchain and ring systems are made. The structure of imidazole-4-aldehyde is discussed in detail in the light of ultraviolet and infrared spectrophotometric data. These data reveal that, contrary to the postulate of Hubball and PymanJ2 the aldehyde does not exist as an enol. Its peculiar properties must ...
