Alina Secrieru1,2, Susy Lopes3, Maria L S Cristiano2, Rui Fausto3. 1. CCMAR and Department of Chemistry and Pharmacy, FCT, Campus de Gambelas, University of Algarve, 8005-039 Faro, Portugal. 2. Department of Chemistry, University of Liverpool, Liverpool L69 7ZD, UK. 3. CQC-IMS, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
Abstract
The prototropic tautomerism in 3(5)-aminopyrazoles was investigated by matrix isolation infrared (IR) spectroscopy, supported by DFT(B3LYP)/6-311++G(d,p) calculations. In consonance with the experimental data, the calculations predict tautomer 3-aminopyrazole (3AP) to be more stable than the 5-aminopyrazole (5AP) tautomer (calculated energy difference: 10.7 kJ mol-1; Gibbs free energy difference: 9.8 kJ mol-1). The obtained matrix isolation IR spectra (in both argon and xenon matrices) were interpreted, and the observed bands were assigned to the tautomeric forms with help of vibrational calculations carried out at both harmonic and anharmonic levels. The matrix-isolated compound (in argon matrix) was then subjected to in situ broadband UV irradiation (λ > 235 nm), and the UV-induced transformations were followed by IR spectroscopy. Phototautomerization of the 3AP tautomer into the 5AP form was observed as the strongly prevalent reaction.
The prototropic tautomerism in 3(5)-aminopyrazoles was investigated by matrix isolation infrn class="Chemical">ared (IR) spectroscopy, supported by DFT(B3LYP)/6-311++G(d,p) calculations. In consonance with the experimental data, the calculations predict tautomer 3-aminopyrazole (3AP) to be more stable than the 5-aminopyrazole (5AP) tautomer (calculated energy difference: 10.7 kJ mol-1; Gibbs free energy difference: 9.8 kJ mol-1). The obtained matrix isolation IR spectra (in both argon and xenon matrices) were interpreted, and the observed bands were assigned to the tautomeric forms with help of vibrational calculations carried out at both harmonic and anharmonic levels. The matrix-isolated compound (in argon matrix) was then subjected to in situ broadband UV irradiation (λ > 235 nm), and the UV-induced transformations were followed by IR spectroscopy. Phototautomerization of the 3AP tautomer into the 5AP form was observed as the strongly prevalent reaction.
Authors: Patrícia S M Amado; Inês C C Costa; José A Paixão; Ricardo F Mendes; Sofia Cortes; Maria L S Cristiano Journal: Molecules Date: 2022-08-24 Impact factor: 4.927