Question

Give an example of a compound which has cyclic trimer structure.

Answer 1

The cyclic trimer of the otherwise unstable species thioformaldehyde is 1,3,5-trithiane. A six-membered ring with alternating methylene bridges and other groups makes up this heterocycle. It's made by combining formaldehyde with hydrogen sulphide.

Complete answer:
Solid $S{O_3}$ have a cyclic trimer structure. As pure $S{O_3}$ gas is concentrated, it forms an ice-like trimer, which is cyclic. This is also known as $y - S{O_3}$. Condensation of pure sulphoxide gas results in the forming of the trimer. The Lewis structure is made up of two dative bonds and two S-O double bonds, with little use of d orbitals.
Sulphur trioxide gas has a trigonal planar strict structure. Sulphur trioxide, which is completely pure, condenses into a trimer as gas .That is, Sulphur trioxide is a gas with a trigonal planar shape and it condenses into a trimer as gas. We also know that Sulphur trioxide is a strong Lewis acid. Hence, Sulphur trioxide is generated when sulphur dioxide is directly oxidised and Sulphur trioxide is a hygroscopic substance. In sulfonation reactions, sulphur trioxide is an important reagent. Sulphur trioxide is generated in situ by sulphuric acid. Hence $S{O_3}$ is formed and it has a cyclic trimer structure.
Hence, Solid $S{O_3}$ has a cyclic trimer structure.

Note:
Remember the following, the valency of sulphur is two, and the valency of oxygen is two. The trigonal planar geometry of sulphur trioxide is unique. Oxidation state of sulphur is $+ 6$.