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

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

JOURNAL OF PHYSICAL CHEMISTRY A

AMER CHEMICAL SOC

Lugar: Washington; Año: 2018 vol. 122 p. 601 - 609

1089-5639

In the present work, we combined solid-state nuclear magnetic resonance (ss-NMR) and single-crystal X-ray diffraction studies to test the stability of gem-diol forms in imidazolecarboxaldehyde isomers and determine the factors that lead to this ?infrequent? functionalization in carbonyl moieties. We found that the position of the carbonyl group had a clear and direct effect on the hydration rate, as only 36% and 5% of 5- and 4-imidazolecarboxaldehydes were hydrated in the same conditions as those in which 2-imidazolecarboxaldehydes were completely hydrated. The trifluoroacetic acid (TFA) was useful not only for the enhancement of the addition of water to the carbonyl group but also for obtaining single-crystals. Interestingly, single-crystals for the gem-diol form of 2-imidazolecarboxaldehyde and hemiacetal form of N-methyl-2-imidazolecarboxaldehyde were isolated and also studied through 1H ss-NMR. However, we observed that the high spinning of the sample produced the reversion of the gem-diol form to its aldehyde. Thus, mass spectrometry and liquid-state NMR experiments were performed to complement the study of the hydration process.