The lithium salt of p-phenylisobutyrophenone (LiPhIBP) exists in tetrahydrofuran (THF) as a mixture of monomer and tetramer contact ion pairs (CLP). The equilibrium constant, K-1,K-4 = 5.0 x 10(8) M-3, indicates that the lithium enolate is primarily tetrameric at higher concentrations, but the monomer is still present in significant amounts even at concentrations typical of synthesis reactions. Alkylation reactions of LiPhIBP with various alkylating agents were investigated in THF at 25 degrees C at concentrations of 10(-3) to 10(-2) M by using UV-vis spectroscopy. The kinetics followed rate laws of 0.50 to 0.30 order in the formal lithium enolate concentration but is first order in the monomer concentration. These rate studies provide direct evidence that the reactive species is the monomer, even when tetramer dominates the equilibrium.