A 1H and 13C nuclear magnetic resonance study of the conformation of aerosol OT in water and hydrocarbon solutions

The conformation of sodium bis(2-ethylhexyl)sulphosuccinate (AOT) in CD3OD, D2O, CDCl3, C6D6 and a[2H8] toluene–D2O microemulsion has been studied using 1H–1H and 13C–1H spin–spin coupling constants. In all systems the AOT headgroup exists predominantly in one unequivocally identified conformation with the ester groups gauche to each other, and the sulphite group trans to one ester group. In the ester groups, the conformation of the CH2—OCO bond is restricted with the carbonyl carbon gauche to both protons. For the OCH2—CH bond in the alkyl chains there are at least two significantly populated conformations. Secondary splittings in 1H and 13C spectra have been attributed to diastereoisomerism of the alkyl chain asymmetric centres. An error in the previously published assignment of the 13C carbonyl spectrum has been corrected. The conclusions of Ueno and coworkers are largely confirmed.