AbstractThe rates of solvolysis of 1,1‐diarylethyl p‐nitrobenzoates and chlorides were determined conductimetrically at 25 °C in 80% (v/v) aqueous acetone. Applying the Yukawa–Tsuno (Y–T) equation, the symmetrical (X = Y) subseries gave a precise additivity relationship for the whole substituent range with a ρsym value of −3.78 and an rsym value of 0.77. While any Y subsets gave statistically less reliable Y–T correlations, the apparent ρ value changed significantly depending on the fixed Y substituents; the ρ value decreases with the more electron‐donating fixed substituents Y, which is compatible with the Hammond shift of the transition state coordinate. Nevertheless, the concave correlations of the More O'Ferrall non‐linearity relationship for any Y subsets are not in line with what is expected from the reactivity–selectivity relationship suggesting an anti‐Hammond shift of transition state. However, we found a precise extended Brønsted relationship between the pK values of 1,1‐diarylethylenes and solvolysis rate process with a constant slope of α = 1.03 ± 0.03. This is direct evidence indicating that there is no significant shift of the transition‐state coordinate over the whole range of substituent change. Copyright © 2002 John Wiley & Sons, Ltd.