Infrared and nuclear magnetic resonance spectroscopic studies of the structure and dynamics of allylic magnesium compounds

Article abstract of DOI:10.1016/0022-328x(95)06014-n

The infrared spectra of allyl- and methallyl-d₂-magnesium bromides have two double bond stretching bands, corresponding to C=CH₂ and C=CD₂ groups in equilibrating allylic isomers. The methylene resonances in the ¹³C NMR spectra of allylmagnesium bromide and chloride and methallylmagnesium bromide are broadened at low temperatures by an exchange process which appears to be the interconversion between the classical unsymmetrical allylic structures. Analogous changes are seen in the spectrum of 1,3-dimethylallylmagnesium chloride and in the proton NMR spectrum of allylmagnesium bromide. Rate constants and activation parameters for the exchange have been determined from the line broadenings. Unlike the Grignard reagent, the methylene resonances of diallylmagnesium in tetrahydrofuran are not significantly broadened at reduced temperature, and the deuterated reagent does not have two distinct double bond stretching bands in the IR spectrum.