THE EFFECTS OF SOLVATION AND POLARIZABILITY ON THE REACTION OF S-P-NITROPHENYL THIOBENZOATE WITH VARIOUS ANIONIC NUCLEOPHILES

Second-order rate constants have been measured spectrophotometrically for the nucleophilic substitution reactions of S-p-nitrophenyl thioben zoate with various anionic nucleophiles including 6 alpha-effect nucle ophiles. A good Bronsted correlation has been observed for the reactio ns with 7 aryloxides. However, p-chlorothiophenoxide and hydroxide ion s exhibit significantly positive and negative deviations, respectively , from the Bronsted plot. The deviations are attributed to the effect of Polarizability and solvation rather than a change in the reaction m echanism. The alpha-effect nuceophiles except highly basic ones demons trate remarkably enhanced nucleophilicity. The effects of solvation an d/or polarizability are proposed to be important for the cause of the alpha-effect.