In contradiction with accepted views about Wurtz coupling reactions during the preparation of Grignard solutions, the highly accurate Volhard titrimetric and the complexometric method show no difference. Checking the amount of coupling product by direct GLC the obtained results are discussed on the basis of a new mechanistic scheme, which assumes the formation of univalent magnesium radicals. These either disproportionate after preparation, or stay bonded as subhalide.

No abstract

Relative reaction rates of fifteen meta and para substituted acetophenones were measured using gas chromatography. With the normal Hammett σ‐values, a linear free energy relationship is found (ρ=+ 0.415), from which strongly conjugative substituents (p. EtO‐, p. MeO‐, p. NMe2‐) deviate. No deviation is found for weak and moderately strong+M substituents. These results are interpreted in the light of a previously proposed (8) reaction mechanism. Resonance contribution can displace the rate‐determining step of the multistep process of the Grignard addition reaction.

The reactivity in the normal Grignard addition reaction is greatly reduced when the ketone is branched in the α‐position. Alkylation in β‐position has only slight effect and in the γ‐position there is no effect at all.