Lithium Quadrupole Coupling Constants and the Structures of Organic Lithium Compounds in Solution

The quadrupole splitting constants (QSC), defined as (1 + ή²/3)^1/2(e²Qq_zz/^h, for⁷Li in lithium arylamides, phenolates, and enolates and for several organolithium compounds in ether and tertiary amine solvents are determined from⁷Li and¹³C spin-lattice relaxation data. The effect of anisotropic rotational diffusion on the apparent values of QSC is considered. Values of QSC range from 40 to 350 kHz. Empirical correlations between QSC and the degree of aggregation and solvation of lithium are presented. Large differences between QSC for tri- and tetracoordinated lithium are noted. A crude model based on a point charge approximation for calculating the principal field gradients reproduces the qualitative features of the empirical correlations. The degrees of solvation of aggregated lithium salts are discussed.