A Quantitative Insight of Substituent Effect in Terms of Reactivity and Nucleophilicity in Rapid Aqueous Iodinations of Monosubstituted Benzene Derivatives Employing Hydrodynamic Voltammetry

Reactivity and nucleophilicity are enlightening aspects of the substituent effect (SE) in most aromatic electrophilic and nucleophilic substitution reactions. Herein, we have quantitatively delved into the reactivity of some monosubstituted benzene derivatives having either an electron donating or withdrawing substituent by exploring the real time progress of their rapid aqueous iodinations at pH 7.4 using iodine solutions devoid of iodide ions chronoamperometrically, employing hydrodynamic voltameter (HV) reinforced with a sensitive Keithley 2450 Digital Source Meter (KDSM). All the reactions are studied in purely aqueous medium using micromolar quantities of reactants, wherein green chemistry principles are adhered, ensuring sustainable development. Voltammograms of the substrates in the reactions were acquired to evince their reduction propensities, these being a quantitative measure of their nucleophilicities. The reactivity of these substrates was evidenced in terms of their specific reaction rates, half-lives, energies of activation, and entropies of activation, while their nucleophilicities were revealed in terms of the half-wave potentials. Unanticipated concomitant kinks in reactivity and nucleophilicity trends have been observed, and a linear mathematical correlation between them has been established in the reactions studied.