| Summary: | Ureido-<i>N</i>-iso-propyl,<i>N</i>’-4-(3-pyridin-2-one)pyrimidine (<b>1</b>) and its 2-methoxy pyridine derivative (<b>1Me</b>) has been designed and prepared. The conformational equilibrium in urea moiety and tautomerism in the pyrimidine part have been investigated by variable temperature and <sup>1</sup>H NMR titrations as well as DFT quantum chemical calculations. The studied compounds readily associate by triple hydrogen bonding with 2-aminonaphthyridine (<b>A</b>) and/or 2,6-bis(acetylamino)pyridine (<b>B</b>). In <b>1</b>, the proton is forced to 1,3-tautomeric shift upon stimuli and keeps it position, even when one of the partners in the complex was replaced by another molecule. The observed tautomerism controlled by conformational state (kinetic trapping effect) opens new possibilities in molecular sensing that are based on the fact that reverse reaction is not preferred.
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