Thiol group

The thiol group, or sulphydryl group or mercaptan group, is the functional group –SH. The prefix "thio" in this, and other functional groups, means that it has a sulfur atom instead of an oxygen (for example, there are also the thioester and thioether groups...). In this case, the ending suffix "ol", tells us that indeed this group is a group derived from an alcohol. That is, instead of the hydroxyl group –OH, we have sulfur in the place of the oxygen. One very important difference with respect to hydroxyl groups is related to the fact that the thiol groups present a weak acid behavior.
Since it has sulfur in its composition, the presence of thiol groups often confers to molecules an unpleasant odor.