Identification of the monoanions and of their complexes with lithium salts possibly formed in solution during the alkylation of lithiated phenylacetonitrile dianions: Infrared spectroscopy and density functional theory calculations

The carbanionic species possibly formed during the first alkylation step of phenylacetonitrile lithiated anion by CH3I and PhCH2Cl in THF-hexane solution and their complexes with the lithium salt formed have been observed by infrared spectrometry and characterized by density functional theory calculations. The spectra of alkylated phenylacetonitrile lithiated anion monomers and dimers have been identified in good agreement with calculations. The wave numbers of the vibrational modes of the alkylated species differ significantly from those of PhCHCNLi species, but do not depend appreciably on the substituent nature. Nevertheless with the methyl substituent, the isomerization equilibrium of the monomer is noticeably shifted toward the bridged (C-lithiated) species. The formation of a heterodimer at the expense of the dimer after addition of LiCl has been confirmed by experiment.