Thiol ($\mathrm{R}-\mathrm{SH}$)

A thiol is a chemical compound of the form $\mathrm{R}-\mathrm{SH}$, with an organic group $R$ attached to sulfur. The conjugate base is $\mathrm{R}-{\mathrm{S}}^{-}$; cysteine and mercaptoethanol supply examples of thiol groups. Two thiol groups can undergo oxidation to form a disulfide bond. ^[ref]