X‑ray Absorption Spectroscopy of Aliphatic Organic Sulfides

Organic sulfides, sometimes called thioethers, are important in a variety of materials with diverse roles in biology and the environment. They also contribute a significant proportion of the sulfur in fossil fuels. We have studied a range of aliphatic sulfides using a combination of sulfur K-edge X-ray absorption spectroscopy and density functional theory calculations. We show that the sulfur K-edge near-edge X-ray absorption spectra of aliphatic organic sulfides comprise two intense transitions in the near-edge spectrum, which can be assigned as 1s → (S–C)­σ* and 1s → (S–C)­π* transitions. These transitions are found to change in a systematic manner in sterically hindered sulfides composed of four-, five- and six-membered rings. Both the 1s → (S–C)­σ* and 1s → (S–C)­π* transitions are sensitive to the presence of strain in the C–S–C angle, shifting to lower values with more strained ring systems. Steric effects can give obtuse C–S–C angles, which are predicted to cause the two transitions to converge to the same energy and even cross over at very obtuse angles.