 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.The release is due to the breaking open of the onion cells and their releasing enzymes called alliinases, which then break down amino acid sulfoxides, generating sulfenic acids.