7Li/31P 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 were studied in THF and HMPA−THF solution. In pure THF, 7 Li NMR line width studies suggest that these species exist as contact ion pairs; HMPA titration 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 31 P and 7 Li NMR spectroscopy. Finally, at 4−6 equiv of added HMPA, 7 Li NMR spectra provide direct evidence for the formation of HMPA-solvated separated ion pairs.