Antiaromaticity

Planar, cyclic hydrocarbon compounds with conjugated double bonds are then anti- aromatic when they have 4n π - electrons ( n = 1, 2, 3 ..). They are thus in contrast to the " first appearances " no aromatics, having no 4n 2 π - electrons have (see Hückel rule). As the prefix " anti- " already makes it clear they are in their behavior sometimes the exact opposite of the aromatics. This is particularly evident in their instability: While aromatics compared to " normal" cyclic hydrocarbon compounds stable ( = less reactive ) are anti - aromatic unstable and settle more or less spontaneously, to lose their Antiaromazität. The structure of the antiaromatics is interpreted as a diradical with very little Mesomeriestabilisierungsenergie.

An example of an anti- aromatic compound, the cyclobutadiene, only at very low temperature ( ≤ 20 K) is stable in a solid matrix. Tri -tert- butylcyclopentadiene, however, is a few hours at 20 ° C resistant. The complex cyclopentadiene eisentricarbonyl is stable at room temperature and serves as a source for the generation of cyclopentadiene.