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Multiparameter correlation of the rate of a [2 + 2] cycloaddition reaction versus solvophobicity parameter and normalized polarity parameter in aqueous solutions
Author(s) -
Gholami M. R.,
Yangjeh A. Habibi
Publication year - 2000
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 - 10.1002/1099-1395(200008)13:8<468::aid-poc258>3.0.co;2-e
Subject(s) - chemistry , aqueous solution , reaction rate constant , solvent , methanol , reaction rate , correlation coefficient , analytical chemistry (journal) , organic chemistry , kinetics , catalysis , physics , statistics , mathematics , quantum mechanics
The second‐order rate constants of the [2 + 2] cycloaddition reaction between diethyl azodicarboxylate and ethyl vinyl ether were obtained spectrophotometrically in various solvents and aqueous solutions of 1,4‐dioxane and methanol at 30 ± 0.1 °C. In all media except aqueous solutions, a very good linear correlation of log k 2 vs E T N (normalized polarity parameter) was obtained ( n = 11, r = 0.991, s = 0.086). Because of the higher polarity of the activated complex relative to the reactants, the rate of the reaction increase with increasing solvent polarity parameter. Dual‐parameter correlation of log k 2 vs π* (dipolarity/polarizability) and α (hydrogen bonding acidity) also gives good results in various solvents ( n = 11, r = 0.985, s = 0.118). Both π* and α have approximately equal effects on the reaction rate. In aqueous solutions of 1,4‐dioxane and methanol, the second‐order rate constants of the reaction increase dramatically with increasing mole fraction of water. A dual‐parameter correlation of log k 2 vs Sp (solvophobicity parameter) and E T N was found in aqueous solutions ( n = 13, r = 0.988, s = 0.165), in which Sp plays an important role in determining the reaction relative to E T N . This model represents a significant improvement in regression coefficient with respect to the single parameter correlation vs Sp or E T N ( r = 0.954 and 0.854, respectively). Similarly to aqueous solutions, a dual‐parameter correlation of log k 2 vs Sp and E T N was obtained in all media ( n = 21, r = 0.987, s = 0.177). Copyright © 2000 John Wiley & Sons, Ltd.