Nucleophilic addition reaction of benzenethiols (PhSH) to 1-(2-nitrovinyl) benzenes ($eta$ NS) in the presence of triethylamine (TEA) has been studied in acetonitrile at 25 ${^{circ}C}$. The rate is first order with respect to [PhSH], [TEA] and [$eta$ NS]. The reaction is found to proceed with the formation of ion-pair between benzenethiol and TEA. A suitable mechanism with the formation of an adduct between ion-pair and substrate in a slow step followed by its rearrangement to 1,2-addition product in a fast step has been proposed and corresponding rate law derived. From the rate law, the rate constants for the interaction between ion-pair and $eta$NS have been evaluated. Interestingly, in both para-substituted substrates and benzenethiols the rate increases with the electron-withdrawing power of the substituents. The positive sign of $ ho_x$ in benzenethiols has been explained. The magnitude of cross-interaction constant, $ ho_{xy}$ is small (0.08). The magnitude of the Hammett $ ho_x$ values is higher than that of the Bronsted, $eta_x$ values for benzenethiols. The kinetic isotope effect, $k_H/k_D$, is found to be greater than unity. A suitable transition state with simultaneous formation of $C_eta$ -H and $B_alpha$ -S bonds involving the ion-pair and $eta$NS in a single concerted step has been proposed to account for these observations.