Nuclear Magnetic Resonance Spectroscopy. Structure and Dynamic Character of Allylic Grignard Reagents

Studies have been made of the nuclear magnetic resonance spectra of several allylic Grignard reagents. The Grignard reagent prepared from γ,γ-dimethylallyl bromide appears best formulated as an equilibrium mixture of γ,γ-dimethylallylmagnesium bromide and α,α-dimethylallylmagnesium bromide, in which the former is the major component. The rate of interconversion of the allylic isomers is rapid on the n.m.r. time scale at room temperature, but slow at -40°