Science, Tech, Math › Science Mercaptan Definition Share Flipboard Email Print Bacsica / 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. 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. Updated October 03, 2019 Definition: Mercaptan is an organic sulfur compound composed of an alkyl or aryl group and a thiol group.General formula: R-SH where R is an alkyl or aryl group. Also Known As: thiol Examples: The amino acid cysteine is a mercaptan. Continue Reading