Structural Determination of Grignard Reagents by Gas Electron Diffraction.

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Two nozzles were designed and made. One was to make gaseous alkyl halides react on the magnesium surface and other one was to make reaction between gaseous magnesium and alkyl halides. They were used in a gas electron diffraction apparatus equipped with a mass spectrometer. Methyl halides, CH_3X (X=Cl, Br and I) , were heated in these nozzles and the reaction products were analyzed using the mass spectrometer. In all the cases, only the pyrolysis products of the alkyl halides were detected and no evidence was found for the formation of Grignard reagents, CH_3MgX.Therefore, it was concluded that in either system of gaseous methyl halide + solid magnesium or gaseous methyl halide + gaseous magnesium, no insertion reaction of magnesium into methyl halide occurs. This conclusion is not consistent with the existing reports based on ab initio calculations and it strongly suggests that the solvation process is playing an important role in formation or stabilization of Grignard reagents.In the next step, a new type of nozzle was designed, with which the solution of Grignard reagent is introduced into the electron diffraction apparatus and is effused as small droplets. When this nozzle was tested by using pure liquid of diethyl ether, the droplets of the sample was observed to be emerging and quickly evaporating at the nozzle end. The diffraction pattern recorded at this condition was found to be identical to that of the gaseous sample. This means that the droplet sample was completely vaporized without forming clusters.Finally, a similar test was carried out by using a diethyl ether solution of Grignard reagent, CH_3I.In this case, however, serious deposition of white substance that might be MgI_2 and CH_3MgCH_3 Happened, which made the electron diffraction experiment impossible. Revision of the experimental condition is pending.