## Wikipedia - Nekekulovská molekula (cs) Wikipedia - Non-Kekulé molecule (en) Wikipedia - Rodniki (pl) Wikipedia - Triangulene (en) Wikipedia - 非ケクレ分子 (ja) biradical

https://doi.org/10.1351/goldbook.B00671
An even-electron @[email protected] with two (possibly delocalized) radical centres which act nearly independently of each other, e.g.
B00671.png
Species in which the two radical centres interact significantly are often referred to as 'biradicaloids'. If the two radical centres are located on the same atom, the species are more properly referred to by their generic names: @[email protected], @[email protected], etc. The lowest-energy @[email protected] of a biradical lies below or at most only a little above its lowest @[email protected] (usually judged relative to $$k_{\text{B}}\ T$$, the product of the @[email protected] $$k_{\text{B}}$$ and the absolute temperature $$T$$). The states of those biradicals whose radical centres interact particularly weakly are most easily understood in terms of a pair of local doublets. Theoretical descriptions of low-energy states of biradicals display the presence of two unsaturated valences (biradicals contain one fewer bond than permitted by the rules of @[email protected]): the dominant @[email protected] bond structures have two dots, the low energy @[email protected] @[email protected] have only two electrons in two approximately nonbonding molecular orbitals, two of the natural orbitals have occupancies close to one, etc. Although this term has been recommended in the past for @[email protected], specialists working in the field prefer the latter term.