Thiyl

Thiyl is a term used in chemistry to denote sulfur-containing species derived from thiols. It can refer to the thiol-derived substituent -SR (a thiyl group, also called sulfanyl) or to sulfur-centered radicals known as thiyl radicals, RS•, formed from thiols R-SH by removal of a hydrogen atom. The concept is the sulfur analogue of hydroxy in oxygen chemistry, highlighting sulfur’s role in these functional units.

Thiyl radicals are generated by homolytic cleavage of S–H bonds in thiols, by photolysis or oxidation of disulfides, or through hydrogen abstraction by other radicals. These radicals are highly reactive and short-lived, participating in various chain-initiating and chain-propagating processes. Typical reactions include addition to carbon–carbon double bonds, hydrogen abstraction from donors, or coupling with another RS• to form disulfides RSSR. In biological systems, thiyl radicals can form on cysteine residues, contributing to disulfide bond formation and protein oxidation.

In practical contexts, thiyl species play roles in organic synthesis, polymer chemistry, and materials science as reactive intermediates in radical reactions and thioether formation. The term thiyl is also used in coordination chemistry to describe thiolate-type ligands bound to metal centers, though “thiolate” is a more common designation in that context. Overall, thiyl species are important for understanding oxidative processes, enzyme mechanisms, and radical-mediated transformations involving sulfur.