Wikipedia
Thioformaldehyde
Thioformaldehyde is the organosulfur compound with the formula CHS. This compound is very rarely observed because it oligomerizes to 1,3,5-trithiane, which is a stable colorless compound with the same formula. Despite its instability under normal terrestrial conditions, the molecule has been observed in the interstellar medium]] and has attracted much attention for its fundamental nature. The tendency of thioformaldehyde to form chains and rings is a manifestation of the Double bond rule.