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Electron transfer reactions (ETR) of tert ‐butyl perbenzoates with dimethyl sulfide: the rates controlled by translational entropy
Author(s) -
Kim Sung Soo,
Lim Sang Hak
Publication year - 2006
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.1099
Subject(s) - chemistry , substituent , reaction rate constant , selectivity , entropy of activation , sulfide , medicinal chemistry , thermal decomposition , hammett equation , kinetics , thermodynamics , stereochemistry , organic chemistry , physics , quantum mechanics , catalysis
Abstract Various tert ‐butyl perbenzoates were prepared according to the known methods. The mixtures of tert ‐butyl perbenzoate and dimethyl sulfide underwent thermolysis at several temperatures (T °C: 80, 90, 100, and 110). The rates of consumption of the peresters ( k obs ) were obtained from ln C 0 / C t = k obs × t where C 0 and C t are the concentration of the perester at time 0 and t , respectively. For example : The decrease of the perester satisfied pseudo first order kinetics, and k obs were determined. k Hom. and k ET were obtained from k obs = k Hom. + k ET [CH 3 SCH 3 ] where [CH 3 SCH 3 ]/[perester] > 10. k ET and its relative rates are produced from plot of k obs against [CH 3 SCH 3 ]. Hammett correlation are plotted against σ and σ+ in which σ is better correlated than σ+. Hammett ρ could be considered selectivity which stays constant irrespective of temperature. The phenomenon is not consistent with reactivity/selectivity principle. The differential activation entropies linearly increase with substituent constant σ to give slope of 2.63 while the similar slope for differential enthalpies shows much lower value of 0.892. The dominance of differential entropic terms clearly indicates the entropy control of the rates. Copyright © 2006 John Wiley & Sons, Ltd.