2.4- Dimethylenecyclobutane-1,3-diyl

BBB = bismethylenebiscyclobutylidene DMCBD = 2,4-dimethylenecyclobutane-1,3-diyl I/O = input and output HL = Heitler and London SC = spin-coupled. 

The sequential removal of H and H+ from isobutene-type structural units (so-called H2+ abstraction ) was also used to generate the radical anion of non-Kekule benzene , i.e. l,3-dimethylenecyclobutane-l,3-diyl (39) (Scheme 11). As shown by Hill and Squires161, this highly unusual, distonic C(,II(, isomer can be produced in pure form by reaction of O with 1,3-dimethylenecyclobutane (38). Working in a flowing afterglow mass spectrometer, subsequent reactions were again used to characterize this radical anion and differentiate it from other ( VdL, isomers. 

Spin-coupled Description of Cyclobutadiene and 2,4-Dimethylenecyclobutane-l,3-diyls Antipairs. 

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