Nuclear magnetic resonance studies on polymer carbanions, 5. Polystyryl carbanion with lithium as counter cation and its dimer model compounds

Oligostyryllithium was synthesized by the reaction of sec-butyllithium with styrene in diethyl ether at ?40°C. Dimer model anions (counter cations: Li and K) of the growing chain ends were synthesized by metallation of 1-methoxy-1,3-diphenylpropane. The structures of the lithium compounds were corroborated by ¹³C NMR spectroscopy and compared with those of the potassium compounds. As for polystyryllithium and its model compounds, the charge density on the α-carbon increased and that on the phenyl ring of the growing end decreased with increasing molecular weight, while, in polystyrylpotassium and its model compounds, the charge density on the α-carbon increased and the one on the phenyl ring did not change with increasing molecular weight. The temperature change of the ¹H NMR spectrum of oligostyryllithium in diethyl ether indicated rotation around the C-1? C_α bond at lower temperatures than in tetrahydrofuran, but the activation energy was the same in both solvents. T₁ values of the phenyl carbons in model compound 2b were one to two orders of magnitude shorter than those of the protonated compound.