Thio
Thio is a chemical prefix used in naming to indicate the presence of sulfur, especially when sulfur replaces oxygen in a compound or serves as a key heteroatom. The term derives from the Greek theion, meaning sulfur, and is used across organic and inorganic chemistry to form sulfur-containing analogues of well-known oxygen-containing structures.
In organic chemistry, thio- denotes sulfur analogues of common functional groups. For example, thiols (R–SH) are
In bioinorganic and biochemistry contexts, thio is often encountered in cofactors and metabolic intermediates, such as
Distinctions are occasionally made between thio- and related prefixes (such as oxo- for oxygen-containing analogues, or