Abstract
Abstract : The proton lineshapes for the CH3 groups of lithium and sodium tetramethylaluminate (LiTMA and NaTMA), observed in the solvents ether, tetrahydrofuran (THF), and 1,2-dimethoxyethane (DME) were used to determine the 27 Al spin-lattice relaxation rate R1. The results are interpreted on the basis of an equilibrium between two kinds of ion pairs, an intimate ion pair in which R1 is large and a solvent separated ion pair in which R1 is small. In ether solution, both LiTMA and NaTMA exist as intimate ion pairs while in DME they exist as solvent separated ion pairs. In the THF solutions, the lineshapes depend significantly upon both temperature and concentration, indicating that significant amounts of both ion-pair species are present. Theoretical equations are derived to fit the observed lineshapes on the assumption that the chemical exchange processes are rapid. From the parameters determined by fitting the lineshapes, estimates are obtained for the relative amounts of the two ion-pair species and also for some of the thermodynamic functions describing the equilibrium in the LiTMA-THF and NaTMA-THF solutions. (Author)
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