(S)-1-(3-Nitrophenyl)ethyl tosylate [(S)-2-OTs] was prepared in > 99% enantiomeric excess and the change in the chiral purity of this compound was monitored during solvolysis in 50:50 trifluoroethanol/water. The barely detectable formation of 0.5% (R)-2-OTs after two half times for the solvolysis reaction was used to calculate a rate constant of k(rac) approximate to 4 x 10(-6) s(-1). This is 80-fold smaller than K-iso = 3.2 x 10(-4) s(-1) for the isomerization that exchanges oxygen-16 and oxygen-18 of 3-(NO2C6H4CH)-C-13(Me)OS(O-18)(2)Tos during solvolysis and 10-fold smaller than the minimum value of k(rac) = 4.6 x 10(-5) s(-1) predicted if isomerization and racemization products form by partitioning of a common ion-pair intermediate of a stepwise reaction. It is concluded that the isomerization reaction proceeds mainly by a pathway that avoids formation of this putative intermediate. It is suggested that the solvolysis reaction of 2-OTs may proceed by a stepwise preassociation mechanism where solvent "reorganization" precedes substrate ionization to form an ion-pair intermediate.