The Effects of Solvation and Polarizability on the Reaction of S-p-Nitrophenyl Thiobenzoate with Various Anionic Nucleophiles

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 thiobenzoate with various anionic nucleophiles including 6 ${\alpha}$-effect nucleophiles. A good Bronsted correlation has been observed for the reactions with 7 aryloxides. However, p-chlorothiophenoxide and hydroxide ions 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 mechanism. The ${\alpha}$-effect nuceophiles except highly basic ones demonstrate remarkably enhanced nucleophilicity. The effects of solvation and/or polarizability are proposed to be important for the cause of the ${\alpha}$-effect.