[11] Characterization of retinylidene iminium salts by high-field 1H and 13C nuclear magnetic resonance spectroscopy

Publisher This chapter describes the preparation and characterization of some retinylidene iminium salts using high-field 1H and 13C NMR spectroscopy. In obtaining an IH NMR spectrum of a retinylidene iminium salt such as 3, a small sample of the salt is dissolved in an inert deuterated solvent, in the absence of any water. The primary objectives in characterizing an iminium salt such as 3 are to ensure that protonation of the imine has occurred and to establish isomeric purity. A tremendous advantage of 'H NMR spectroscopy is that it allows for the identification of isomeric forms of retinylidene iminium salts in a single sample. The chapter describes the characterization of the 11-cis isomer that is accomplished primarily through the location and multiplicity of the C-15-H and C-11-H resonances.