Density functional theory calculations of stabilities of various aggregates of lithium 2-methoxyethoxide (MEO-Li), methyl alpha-lithioisobutyrate (MIB-Li), and their mixtures show that hexameric structures of prismatic type are most stable. The calculated NMR shifts at the alpha-carbon atoms of these aggregates correctly reproduce the experimental dependence of the shifts on the molar ratio MEO-Li/MIB-Li. Since these mixtures are models for the active center in the anionic polymerization of methyl methacrylate (MMA), it is demonstrated that some of these mixed aggregates are able to coordinate an MMA molecule. The resulting complex is very stable and has a geometry suitable for the monomer addition reaction, i.e., the bond formation between the MIB-Li alpha-carbon and the monomer vinyl group.