Ethanethiol
Ethanethiol, commonly known as ethyl mercaptan, is a colorless gas or clear liquid with a distinct odor. It is an organosulfur compound with the formula CH3CH2SH. Abbreviated EtSH, it consists of an ethyl group (Et), CH3CH2, attached to a thiol group, SH. Its structure parallels that of ethanol, but with S instead of O. The odor of EtSH is infamous. Ethanethiol is more volatile than ethanol due to a diminished ability to engage in hydrogen bonding. Ethanethiol is toxic. It occurs naturally as a minor component of petroleum, and may be added to otherwise odorless gaseous products such as liquefied petroleum gas (LPG) to help warn of gas leaks. At these concentrations, ethanethiol is not harmful.