The association behavior of the etilefrine HCl was investigated by
1H NMR spectroscopy. Figure 4 shows 1H NMR spectra of the aromatic
protons at different concentrations of etilefrine HCl. The figure
shows an upfield shifts on increasing the concentration. The direction
and magnitude of the chemical shift provides an idea about
the changes in the aromatic protons environment and to what
extent they are involved the association process [6,7]. The chemical
shift changes by 0.149, 0.149, 0.12 and 0.14 ppm for H5, H4,
H2 and H6 respectively on increasing the concentration from 0.01
to 0.2 mol kg1. The proton shifts upon micellization are generally
due to an intermolecular aromatic ring current effect [6,7].