Dimensiosolvatic Effects. IV. Topomerization in Alkyl <i>α</i>-Chlorobenzyl Ethers and Insights into Mechanisms of Their Thermolyses

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  • Michinori Oki
    Department of Chemistry, Faculty of Science, Okayama University of ScienceRidaicho, Okayama 700
  • Hiroshi Ikeda
    Department of Chemistry, Faculty of Science, Okayama University of ScienceRidaicho, Okayama 700
  • Hiromichi Miyake
    Department of Chemistry, Faculty of Science, Okayama University of ScienceRidaicho, Okayama 700
  • Hirohito Mishima
    Department of Chemistry, Faculty of Science, Okayama University of ScienceRidaicho, Okayama 700
  • Shinji Toyota
    Department of Chemistry, Faculty of Science, Okayama University of ScienceRidaicho, Okayama 700

説明

<jats:title>Abstract</jats:title> <jats:p>Rates of topomerization in α-chlorobenzyl ethyl ether and its p-methyl as well as p-methoxy derivatives were determined in various solvents by the dynamic NMR method. The topomerization process was deduced to be ionic because the rates are enhanced in polar solvents as well as by electron-donating substituents. Concentration dependence study of the topomerization in carbon tetrachloride revealed that the observed process is unimolecular; the rates are not affected by concentration of the substrate if the concentration is lower than 0.2 mol L−1. The rates of topomerization are smaller for solutions in bulky solvents than in small solvents, the effects being clear for compounds with electron-donating substituents. The key feature of the kinetic parameters is that the entropy of activation is large and negative for all the solvents examined. The reaction mechanisms are discussed on the basis of these data. The effects of the molecular size of the solvent, dimensiosolvatic effects, are attributed to the effectiveness of the solvation in the formation of ion pairs. The results show that thermolyses of alkyl α-chlorobenzyl ethers are much slower reactions than the ionization. The nature of the reaction is discussed.</jats:p>

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