A trimer of acetaldehyde (C6H12O3), prepared by polymerization of acetaldehyde with hydrochloric and sulfuric acids. It has sedative and hypnotic properties.

a colorless liquid (a cyclic trimer of acetaldehyde) that is used as a sedative and a solvent

Paraldehyde is the cyclic form of three acetaldehyde molecules (a trimer). A colourless to pale yellow pungent liquid, it is sparingly soluble in water and highly soluble in alcohol. It has industrial and medical uses.