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Activation energy barriers in the molecular relaxation dynamics of Li + interacting with acyclic and cyclic polyethers in acetonitrile
Author(s) -
Xu Meizhen,
Eyring Edward M.,
Petrucci Sergio
Publication year - 1991
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550230707
Subject(s) - chemistry , acetonitrile , relaxation (psychology) , activation energy , solvent , molecular dynamics , spectral line , computational chemistry , organic chemistry , psychology , social psychology , physics , astronomy
Ultrasonic relaxation spectra of LiClO 4 plus the open chain polyether triglyme (TG) at C LiClO4 ≃ 0.8 M, molar ratio R = [TG]/[LiClO 4 ] = 1, and at temperatures of 15, 25, 35, and 45°C in dry acetonitrile are reported. Corresponding spectra for LiClO 4 plus the macrocycle 12‐crown‐4 (12C4) at R = [12C4]/[LiClO 4 ] = 1, at 10, 15, 20, 25, 30, and 40°C, and C LiClO4 = 0.32 M in acetonitrile are also reported. Both relaxation envelopes, for the two systems, have been fitted by two Debye relaxation processes and interpreted by the Eigen‐Winkler reaction scheme:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm Li}^ + \cdots {\rm PE} \mathop{\rightleftharpoons}\limits^{k_1}_{k_-1}{\rm LiPE}^ + \mathop{\rightleftharpoons}\limits^{k_2}_{k_-2} ({\rm LiPE})^ + $$\end{document}where “PE” symbolizes the polyether, Li + … PE is a solvent separated species and LiPE + and (LiPE) + are two complex species. The temperature dependence of the relaxation spectra permits the calculation of the activation parameters for the forward and reverse processes for the system LiClO 4 + TG and for one of the two processes for the LiClO 4 + 12C4 system. Comparisons between the two sets of data lead to the conclusion that the much slower second relaxation process, in the case of the macrocycle, is attributable to a combination of an enthalpic and an entropic effect on the energy barrier for the present systems.