Schlenk hydrocarbons

In view of the subsequent work, the content of the actual monomeric diradicals in Schlenk hydrocarbons was rather miniscule. For Gomberg radical, the percentage of the monomeric radical in dilute solutions is relatively small (K msoc 10-4 M-1 at 293 K) 31 thus, the content of the monomer for the corresponding diradicals is likely to be much smaller that less than few percent for triphenylmethyl in dilute solutions. Also, the reported violet color of 8 is unlikely to correspond to monomeric diradical.63... 

Rajca, A. and Rajca, S. (1998). Alkyl-substituted Schlenk hydrocarbon diradicals with triplet and singlet ground states in frozen solutions. J. Chem. Soc. Perkin 2, 1077-1082... 

Early investigations indicated that consisted of less than 0.2% biradical 3, but that compound the Chichibabin hydrocarbon, was 5-10% biradical based upon p to jor-hydrogen conversion or esr. However a more recent esr stud has led to the conclusion that the paramagnetic species in is in fact the dimer. On the other hand because of their reactivity and the impossibility of drawing classical valence bond structures, with no unpaired electrons, the Schlenk hydrocarbons ( > ) were considered to be diradicals. 

Historically, it took quite some time before the diradical paradox associated with the Chichibabin [9], Thiele [10] and Schlenk [11] hydrocarbons was resolved by epr experiments and by the reasoning based on these topological considerations (Platz, 1982) only the last hydrocarbon was concluded to have a ground triplet state (Kothe et al., 1970 Luckhurst et al., 1971). 

However, it soon became clear that matters might not be so simple. There is a fundamental difference in the connectivity of the n centers in TME and that in TMM. Hiickel recognized a similar difference in the case of the two Schlenk-Brauns hydrocarbons 1 and 2, and the theory was put on a modern basis and generalized by Borden and Davidson. ... 

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