Generation and Stability of the gem-Diol Forms in Imidazole Derivatives Containing Carbonyl Groups. Solid-State NMR and Single-Crystal X-ray Diffraction Studies

LÁZARO-MARTÍNEZ, JUAN MANUEL; VEGA, DANIEL; LÁZARO-MARTÍNEZ, JUAN MANUEL; VEGA, DANIEL; MONTI, GUSTAVO ALBERTO; BYRNE, AGUSTÍN JESÚS; MONTI, GUSTAVO ALBERTO; BYRNE, AGUSTÍN JESÚS; CHATTAH, ANA KARINA; CRESPI, AYELÉN FLORENCIA; CHATTAH, ANA KARINA; CRESPI, AYELÉN FLORENCIA

JOURNAL OF PHYSICAL CHEMISTRY A

AMER CHEMICAL SOC

Año: 2018 vol. 122 p. 601 - 609

1089-5639

The stability of gem-diol forms in imidazolecarboxaldehyde isomers was studied by solid-state nuclear magnetic resonance (ss-NMR) combined with single-crystal X-ray diffraction studies. These methodologies also allowed determining the factors governing the occurrence of such rare functionalization in carbonyl moieties. Results indicated that the position of the carbonyl group is the main factor that governs the generation of geminal diols, having a clear and direct effect on hydration, since, under the same experimental conditions, only 36% of 5-imidazolecarboxaldehydes and 5% of 4-imidazolecarboxaldehydes were hydrated, as compared to 2-imidazolecarboxaldehydes, with which a 100% hydration was achieved. Not only did trifluoroacetic acid favor the addition of water to the carbonyl group but also it allowed obtaining single crystals. Single crystals of the gem-diol and the hemiacetal forms 2-imidazolecarboxaldehyde and N-methyl-2-imidazolecarboxaldehyde, respectively, were isolated and studied through 1H ss-NMR. Mass spectrometry and solution-state NMR experiments were also performed to study the hydration process.