Thioenols (also known as alkenthiols) are alkenes with a thiol group affixed to one of the carbon atoms composing the double bond. Alkenes with a thiol group on both sides of the double bond are called enedithiols. Deprotonated anions of thioenols are called thioenolates.
The C=C double bond with adjacent thiol gives thioenols and enedithiols their chemical characteristics, by which they present keto-enol tautomerism. In keto-enol tautomerism, thioenols interconvert with thioketones or thioaldehydes.
The words thioenol and alkenthiol come from the words "alkene" (or just -ene, the suffix given to C=C double bonded alkenes) and "thiol" (which represents the thioenol's thiol group).
Thioketo-thioenol tautomerism
Thioenols interconvert with thiocarbonyl compounds that have an α-hydrogen, like thioketones and thioaldehydes. The compound is deprotonated on one side and protonated on another side, whereas a single bond and a double bond are exchanged. This is called keto-enol tautomerism.