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.