Inductive and field effects in aromatic substitution. Part VII. Hydrogen-isotope exchange in a bridged anthracene derivative carrying a nitrogen pole

Abstract

The ¹H n.m.r. spectra of trans-ll-amino-9, 10-dihydro-12-methyl -9, 10-ethanoanthracene (III) in chloroform solutions containing varying amounts of the shift reagent Eu(dpm)₃ show an almost complete separation of the peaks corresponding to the aromatic protons. These peaks have been divided into sets corresponding to the two aromatic rings by spin-decoupling and assigned almost completely by use of the equation for pseudo-contact interactions. This identification has been used to study aromatic hydrogen–deuterium exchange in solutions of (III) in the mixed solvent CF₃CO₂D–D₂SO₄–D₂O. The extent of exchange has been calculated from the n.m.r. spectra of neutralised samples of the reaction mixture. The kinetic results indicate that reaction occurs through the conjugate acid of (III) and that the NH₃ pole deactivates both rings to a similar extent, despite the fact that the distances of the pole from the centres of two rings are very unequal (3.5 and 5.2 Å). Approximate partial rate factors have been calculated for exchange in the conjugate acid of (III).