Thiol compounds, also known as mercaptans, are organic molecules that contain a sulfur atom bonded to a hydrogen atom (-SH group). They are similar to alcohols, which have a hydroxyl group (-OH), but the presence of sulfur gives thiols distinct properties. Thiols are often characterized by their strong, unpleasant odors, which can be reminiscent of rotten eggs or garlic. These compounds play important roles in various biological processes and are found in many natural substances. For example, cysteine is an amino acid that contains a thiol group and is essential for protein structure and function. Thiols are also used in industrial applications, such as in the production of rubber and as additives in petroleum products.