ESR spin concentration

Table 7.13 ESR Spin Concentration in Plasma Polymers and Glass Substrates...

Benzene is most difficult to convert to an anion radical nevertheless, with potassium at — 80°C in DME the anion radical of benzene can be identified by ESR. Spin-concentration measurements on benzene in 2 1 by volume of THF DME with Na-K alloy at — 83°C show that at equilibrium only ca. 0.1 % benzene is converted to radical anion. Benzene also forms an anion radicaF by ESR with Rb and Cs in THF and DME, but not with Na or Li in THF-DME. Alkyl substitution destabilizes the radical anions as prepared with Na-K in THF-DME at — 100°C, with destabilization increasing with size [CH3 < CH CHj < CH(CH3)2 < C(CH3)3] and with numbers of such groups . In contrast, Si(CH3)3, Ge(CH3)3, CN and NO2 groups stabilize their benzene radical anions. Radical-anion formation even in benzene, toluene, or mesitylene with potassium can be brought about by addition of dicyclohexyl-18-crown-6 , 18-crown-6 or [2.2.2]cryptate at RT or lower. Radical anions may be prepared similarly from Rb and Cs, but not from Na with 18-crown-6 or [2.2.2]cryptand . The yield or how long such solutions are stable is not known. 

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