Li-7/P-31 NMR studies of lithiated arylacetonitriles in THF-HMPA solution:Characterization of HMPA-solvated monomers, dimers, and separated ion pairs

The structures of lithiated phenylacetonitrile and 1-naphthylacetonitrile w ere studied in THF and HMPA-THF solution. In pure THF, Li-7 NMR line width studies suggest that these species exist as contact ion pairs; HMPA titrati on studies confirm this conclusion. In the presence of 0.25-2 equiv of HMPA , HMPA-solvated monomeric and dimeric contact ion pairs are detected by P-3 1 and Li-7 NMR spectroscopy. Finally, at 4-6 equiv of added HMPA, Li-7 NMR spectra provide direct evidence for the formation of HMPA-solvated separate d ion pairs.