where k and kHrate constants for a model reaction of the studied compound and parent benzoic acid (12a) derivatives, Ka and KaH dissociation constants of the studied molecule and parent benzoic acid 12a, reaction rate constant, σ = Log(Ka/KaH)substituent constant (Hammett constant). Hammett constants σ measure the magnitude of the substituent electronic effects, thus allowing positioning new functional groups among the known ones in terms of their electronic properties. To achieve this for the 3,3-diFox moiety, we have studied 14 psubstituted benzoic acids 9, 12a-p (9 -with known σ values of the para substituent, and 5with yet unreported ones, Table in the Supporting Information). Based on the previously established acidity data shown in Figure , the σ values were calculated. The obtained results for the compounds with known σ values was in good agreement with previously reported. In addition to that, kinetic experiments were performed following the methodology reported by Keenan and colleagues. For this purpose, p-nitrophenolate esters 14a-p were synthesized from benzoic acids 12a-p via acyl chloride activation, and the kinetics data of the ester hydrolysis upon action of aq NaOH were studied by UV-Vis spectrophotometry. The obtained logarithmic relative rate constants Log(k/kH) were plotted against calculated Hammett constant values  and linearized using the least square method (Figure ). A good linear correlation was found (R 2 =0.953); the obtained ρ value was slightly lower than the previously reported (1.7 vs. 2.1-2.4 ), which can be related to differences in the experiment conditions. According to the obtained Hammett constant value (σ = 0.24), the 3,3-diFox functional group can be considered a weak electron acceptor, comparable to chlorine (14p, 0.29) and significantly less pronounced than CF3 (14i, 0.68) or CO2Me (14o, 0.70) groups.