Abstract The kinetics of reactions between Y-benzenesulfonyl chlorides and X-pyridines in methanol at 35.0 C were investigated. Strong para π-acceptors, X= p-CN and p-COCH 3, give good linear fits to Brønsted-type plots with low β X (= 0.32–0.45) but show positive deviations from linear Hammett plots (ρ X=− 1.98 to− 2.79). Excellent linear Hammett plots are obtained with substituent variations in the substrate with ρ Y= 0.6–1.0 which are ...