Science, Tech, Math › Science Thiol Definition Share Flipboard Email Print MOLEKUUL / SCIENCE PHOTO LIBRARY / Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated October 02, 2019 Definition: Thiol is an organic sulfur compound composed of an alkyl or aryl group and a sulfur-hydrogen group.General formula: R-SH where R is an alkyl or aryl group. The S-H group is also known as a thiol group. Also Known As: mercaptan Examples: The amino acid cysteine is a thiol.