NMR Studies of Ion Solvation in Non-Aqueous Solvents

It is not surprising that NMR was also applied to the study of cation solvation in non-aqueous media. Most solvent molecules contain protons, but in the case of 

Another method of examining ion-solvent interactions is to study the chemical shifts of the solute ions. This type of investigation has been carried out for the Li +, 2 Na+, and TP cations and for the CP, Br , and P anions. 

Solvation of the halide ions in various solvents has been studied by measuring the chemical shifts for Cl , Br , and 1 in water and several other polar solvents [23]. The chemical shifts are strongly solvent dependent and correlate to the UV absorption band energy corresponding to charge transfer to the solvent. 

Polar molecular solutes have been used to probe the donor-acceptor properties of polar solvents. chemical shifts have been measured for interaction between trifluoroiodomethane and the solvent molecule as electron pair donor [24]. As interaction between the donor molecule and the iodine atom in this molecule increases, electron density at the fluorine atoms increases with a resulting positive chemical shift in the NMR signal. An excellent correlation between these shifts and the Gutmann donor number was reported [24]. 

The chemical shifts in triethylphosphine oxide measured in polar solvents is used to define the acceptor number scale for solvent acidity [25]. In this case, the oxygen atom in the P=0 bond acts as an electron pair donor to the solvent as a Lewis acid. The resulting inductive effect lowers the electron density at the phosphorus atom and results in a chemical shift which depends on solvent acidity. 

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