Free ion-pair equilibria

Winstein et al. [47] have shown conclusively that many organic ionic materials (R X ) in a suitable solvent can exist in at least three forms, a contact (or intimate) ion pair, a solvent separated ion pair, and free solvated ions, e.g. 

The value of, the ion pair dissociation constant, varies according to the nature of R and X , the solvating and dissociating ability of the solvent employed and the temperature. Dennison and Ramsey [48] have treated quantitatively the effect of solvent and have shown the following relationship to hold  

Thus in ionic polymerizations generally, in addition to the difficulty of deciding the chemical nature of the species involved in initiation, propagation etc., there is also the problem of the physical nature of each in relationship to its counter-ion. 

Fortunately there is available a simple conductance technique for monitoring ion pair—free ion equilibria, which, while being unable to give information about different ion pairs, readily produces data on the proportion of free ions to all ion pairs. The equilibrium is treated as approximating to the dissociation of a weak electrolyte, e.g. acetic acid in water. 

For such equilibria Ostwald s Dilution Law represents, fairly accurately, the behaviour of free and paired species, viz. 

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