A density functional theoretical study of the influence of cavities and water molecules on tautomerism: the case of pyridones and 1,2,4-triazoles linked to crown ethers and esters

The tautomerism of pyridones and 1,2,4-triazoles related to two crown ethers and two crown esters derived from these heterocycles was studied theoretically. For the four macrocycles, Bradshaw identified a single tautomer by X-ray crystallography. To rationalize these findings, a series of calculations from simple models to crown derivatives have been carried out. The most interesting case concerns the observation, for the first time, of a 4H-1,2,4-triazole tautomer. To explain this result it was necessary to calculate the whole crown ester plus a caged water molecule was necessary.