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Substituent effects in solvolysis of 1,1‐diphenylethyl p ‐nitrobenzoates. Symmetrically disubstituted and monosubstituted systems
Author(s) -
Fujio Mizue,
Uddin Md. Khabir,
Kim HyunJoong,
Tsuno Yuho
Publication year - 2002
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.484
Subject(s) - solvolysis , chemistry , substituent , additive function , reactivity (psychology) , medicinal chemistry , selectivity , stereochemistry , reaction rate constant , acetone , yukawa potential , aqueous solution , transition state , organic chemistry , kinetics , hydrolysis , quantum mechanics , catalysis , medicine , mathematical analysis , physics , alternative medicine , mathematics , pathology
The 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 ρ sym value of −3.78 and an r sym 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 p K R +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.