syklobutadienin

Cyclobutadiene is a highly reactive organic compound with the chemical formula C4H4. It is a cyclic molecule containing four carbon atoms arranged in a square, with each carbon atom bonded to one hydrogen atom. The key feature of cyclobutadiene is its conjugated system of four pi electrons within the four-membered ring.

According to Hückel's rule, aromatic compounds are characterized by having (4n+2) pi electrons, where n is an integer. Cyclobutadiene, with its four pi electrons, does not satisfy this rule, as 4 is not of the form 4n+2 for any integer n. This deviation from aromaticity contributes significantly to its instability.

In its neutral state, cyclobutadiene is a diradical, meaning it has two unpaired electrons. This makes it very prone to dimerization and other reactions to achieve a more stable electronic configuration. It can exist as a triplet or a singlet state, with the triplet state being more stable.

Due to its extreme instability, cyclobutadiene is not typically isolated or stored as a pure compound. It is usually generated in situ as a transient intermediate in chemical reactions. Its chemistry is often studied through its derivatives, such as cyclobutadiene iron tricarbonyl, where the cyclobutadiene ring is stabilized by coordination to a metal. These metal complexes allow for the study of cyclobutadiene's properties and reactivity in a controlled manner. The concept of cyclobutadiene has been instrumental in the development of understanding aromaticity and antiaromaticity in organic chemistry.