Structure des Complexes de Meisenheimer Complexes de Courte Duree de Vie et Complexes Stables Formes par Action des Ions Méthoxydes sur les Dinitro-4,6 Anisoles X-2 Substitues

The NMR study of the reaction of methoxide ions on several substituted 2-X-4,6-dinitroanisoles (X = F, Cl, CF₃, CN) permitted the identification of various Meisenheimer complexes formed by the attack of CH₃O^? ions on the non-substituted 5- and 3-carbons. The shortlived 1,5- and 1,3-complexes undergo a fast conversion to the stable 1,1-complexes. The chemical shifts of anisoles and complexes are dependent on electronic and steric effects of the X-substituent. The influence of the negative charge held by the ring and the geometrical changes of the skeleton are shown by a comparison between the NMR parameters of anisoles and the corresponding complexes. When X = F, a study of the relative signs of the coupling constants shows that ³J(F? H) and ⁵J(F? H) are of opposite signs for the anisole and the 1,1-complex.