jp1c04081_si_001.pdf (2.05 MB)
Download fileEvidence of IR-Induced Chemistry in a Neat Solid: Tautomerization of Thiotropolone by Thermal, Electronic, and Vibrational Excitations
journal contribution
posted on 20.07.2021, 16:16 authored by Nelson
A. M. Pereira, Cláudio M. Nunes, Igor Reva, Rui FaustoThiotropolone 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 (λ ≥ 400 nm) leads to thione-enol →
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 ∼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.