Date of Award

1982

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

The behavior of the system NaAlEt(,4)-benzene-HMPA as a function of the mole ratio HMPA:NaAlEt(,4) has been studied via equivalent conductance measurements, viscosity measurements and ('23)Na, ('27)Al and ('1)H nmr spectroscopy. This system has the property of forming two immiscible liquid phases. Therefore a careful analysis of the dependence of the lower phase volume on the mole ratio was undertaken. Additionally the uptake of benzene in the lower phase can be followed via nmr integration. The volume studies indicate a similarity in behavior of the anionic organoaluminum "liquid clathrate" compounds. The formation of two liquid phases has been related to the extent of aggregation in this system. The temperature dependence of the equivalent conductance has yielded an activation energy of ionic mobility which can also be related to the extent of aggregation. From these data, it is apparent that a major change in the solute structure occurs at a ratio of 2.5:1 HMPA:NaAlEt(,4). At higher ratios the aggregate breaks up. This break up can be attributed to the formation of a stable solvent bridged complex of stoichiometry {Na(,2)(.)5HMPA}('2+). The interpretation of quadrupole-electric field gradient spin-lattice relaxation mechanism in the ('23)Na nmr spectra implies a stepwise complexation process with HMPA. It was observed that the molecular correlation time, (tau)(,c), of the sodium ion can be approximated by the Debye-Stokes formula for the rotational correlation of a particle in solution. The ('27)Al spin-lattice relaxation time is also primarily due to a quadrupole-electric field gradient interaction. The correlation time of the ('27)Al nucleus results from an entirely different motional process than for the ('23)Na. The proton nmr lineshape of the methylene resonance has been shown to result from the scalar coupling of the protons to the quadrupolar ('27)Al nucleus. Since the ('27)Al relaxation time has been shown to be strongly dependent on ion-ion interactions, the proton nmr lineshape is a sensitive probe of the ion pair type.

Pages

137

Share

COinS