TRAPPING OF COUNTERIONS AND WATER ON THE SURFACE OF CATIONIC MICELLES

The concentration ratios of three nucleophiles, bromide and chloride i ons and water, at the micellar surface were determined from the yields of trans-1,2-dibromocyclohexane, trans-1-bromo-2-chlorocyclohexane, a nd trans-2-bromocyclohexanol, respectively, products of the brominatio n of cyclohexene in aqueous (i) cetyltrimethylammonium bromide (CTAB), (ii) cetylpyridinium bromide (CPyB), and (iii) cetylpyridinium chlori de (CPyC), with added NaX (X = Br-, Cl-). The generally small values o f [X(-)]/[H2O] obtained are attributed to a highly ordered interfacial structure in which the halide ions occupy well defined positions. A s phere to rod transition caused by the addition of NaX for all the surf actants was followed by the variation of the ratio [X(-)]/[H2O] and by H-1 NMR.