Evidence of IR-Induced Chemistry in a Neat Solid: Tautomerization of Thiotropolone by Thermal, Electronic, and Vibrational Excitations

Pereira N. A. M., Nunes C. M., Reva I., Fausto R.

JOURNAL OF PHYSICAL CHEMISTRY A, vol.125, no.29, pp.6394-6403, 2021 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 125 Issue: 29
  • Publication Date: 2021
  • Doi Number: 10.1021/acs.jpca.1c04081
  • Journal Name: JOURNAL OF PHYSICAL CHEMISTRY A
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Academic Search Premier, Applied Science & Technology Source, Aqualine, Aquatic Science & Fisheries Abstracts (ASFA), Artic & Antarctic Regions, Chemical Abstracts Core, Chimica, Compendex, Computer & Applied Sciences, EMBASE, INSPEC, MEDLINE
  • Page Numbers: pp.6394-6403
  • Istanbul Kültür University Affiliated: Yes

Abstract

Thiotropolone isolated in argon and xenon matrices (as monomers) or in a neat solid (as the crystalline or amorphous state) at low temperature was found to exist only in the thione-enol form. Visible light irradiation (lambda >= 400 nm) leads to thioneenol -> thiol-keto tautomerization in matrices and under neat solid conditions at 15 K. The assignment of the IR spectra of the two thiotropolone tautomers (thione-enol and thiol-keto) was carried out with the support of B3LYP/6-311+G(2d,p) computations. The thiol-keto form generated in situ in a neat solid was found to tautomerize back to the thione-enol upon annealing up to 100 K. Gaussian-4 (G4) computations estimate that such a tautomerization process has an energy barrier of, similar to 25 kJ mol(-1), which is consistent with the observations. Moreover, it was found that narrowband IR irradiation of the thiol-keto form in a neat solid, at the frequency of its CH stretching overtones/combination modes, also induces tautomerization to the thione-enol form. Such a result constitutes an important demonstration of vibrationally induced chemistry under neat solid conditions.