Spectres infrarouges et raman des organomagnesiens EtMgX·2Et2O (X = Br,I) cristallises et dissous dans l'ether ethylique

The infrared and Raman spectra of the low-temperature polycrystalline organomagnesium compounds, C₂H₅MgI·2(C₂H₅)₂O and C₂H₅MgBr·2(C₂H₅)₂O and of some deuterated derivatives, C₂H₅MgBr·2(C₂D₅)₂O, CD₃CH₂MgBr·2(C₂H₅)₂O, CH₃CD₂MgBr·2(C₂H₅)₂O and C₂D₅MgBr·2(C₂H₅)₂O have been investigated in the 4000-100 cm^?1 region. An assignment is given for most intramolecular fundamentals of the gauche—gauche isomer of coordinated ether molecules and the effect of coordination on ether frequencies is discussed. The fifteen fundamentals of the “isolated” ethyl group are identified and their frequencies are correlated with those of some hydrocarbons and similar organometallic compounds. The magnesium—ligand stretching vibrations, ν(MgC), ν_asym(MgO₂), ν_sym(MgO₂), ν(MgBr), and ν(MgI) are observed at 485, 317, 301, 248 and 224 cm^?1, respectively; the MgC, MgO and MgBr bond force constants are estimated and correlated with some other structural parameters. The structure of the mixed organomagnesium compound C₂H₅MgBr·2(C₂H₅)₂O in pure liquid state and in ether solution is discussed on the basis of the corresponding Raman spectra. Ethylmagnesium bromide is found to be monomeric in diethyl ether even at high concentrations.