Insights into the Nature of the Chemical Bonding in Thiophene-2-thiol from X‑ray Absorption Spectroscopy

Thiophenes are the simplest aromatic sulfur-containing compounds; they are widespread in fossil fuels and a variety of natural products, and they have vital roles in determining characteristic aromas that are important in food chemistry. We used a combination of sulfur K-edge X-ray absorption spectroscopy and density functional theory to investigate the chemical bonding in the novel sulfur-containing heterocycle thiophene-2-thiol. We show that solutions of thiophene-2-thiol contain significant quantities of the thione tautomer, which may be the energetically preferred 5<i>H</i>-thiophene-2-thione or the more accessible 3<i>H</i>-thiophene-2-thione