Ion pair aggregates and reactions; experiment and theory

Two methods have been developed for determining the aggregation equilibrium constants of lithium enolates based on the change in UV-vis spectrum with concentration and the effect of aggregation on proton-transfer equilibria. Dimers and tetramers are common. Substitution alpha to the carbonyl group generally reduces aggregation. Kinetic studies show that S(N)2 alkylations generally occur with the monomers, even in the presence of large amounts of aggregate. The qualitative chemistry is well modeled by ab initio computations at the HF level with modest basis sets; in these studies solvation is modeled by a combination of coordination of lithium cation with an ether oxygen and the electrostatic interaction of the resulting dipoles and quadrupoles with the solvent dielectric continuum.