S-H rotamerization via tunneling in a thiol form of thioacetamide


Gobi S., Nunes C. M., Reva I., Tarczay G., Fausto R.

PHYSICAL CHEMISTRY CHEMICAL PHYSICS, vol.21, no.31, pp.17063-17071, 2019 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 21 Issue: 31
  • Publication Date: 2019
  • Doi Number: 10.1039/c9cp03417j
  • Journal Name: PHYSICAL CHEMISTRY CHEMICAL PHYSICS
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.17063-17071
  • Istanbul Kültür University Affiliated: Yes

Abstract

Rotamerization of a hydroxyl (O-H) group by tunneling is well-known and has been extensively studied. On the other hand, similar tunneling processes for the thiol (S-H) group have not been reported yet. In this work, the imino-thiol forms of thioacetamide were studied in cryogenic matrices (Ar, Xe) after UV-irradiation of the common amino-thione form of the compound. Four different imino-thiol forms were generated, corresponding to the cis or trans thiol (C/T) conformers of the two imino isomers (syn and anti; s/a). Noteworthy, the syn-cis (sC) imino-thiol form was found to convert spontaneously to the syn-trans (sT) form (with a half-life of 80 min), in a process whose reaction rate is independent of the temperature (i.e., at 11 or 20 K). Such conformational transformation represents the first experimental observation of an S-H rotamerization occurring by tunneling. Computations based on the Wentzel-Kramers-Brillouin formalism predict a tunneling half-life for the S-H rotamerization of syn-imino sC to sT on the time scale of minutes, in agreement with the experimental observations.