 Syn-Propanethial-S-oxide

"syn"-Propanethial "S"-oxide (C3H6OS), a member of a class of organosulfur compounds known as thiocarbonyl "S"-oxides (formerly "sulfines"), is a volatile liquid that acts as a lachrymatory agent (triggers tearing and stinging on contact with the eyes).The chemical is released from onions, "Allium cepa", as they are sliced.