13C-13C NMR coupling constants in substituted allylic ion-pairs of the type occurring in anionic diene polymerization

¹³C-¹³C NMR coupling constants have been measured on the 1:1 adduct of tert-butyllithium and butadiene, a model for the active centres in the anionic polymerization of butadiene. Solutions in three solvents in which solvation and aggregation properties differ were studied, tetrahydrofuran, diethyl ether and benzene. The 2-methyl- substituted analogue, more appropriate for isoprene type systems was also converted to the potassium salt and a comparison was made of the effect of counter ion. Ion-pair structure is discussed in terms of these measurements.