A Study on the Ionic Dissociation Rate of $\alpha$-Chlorobenzyl Ethyl Ether by Dynamic NMR Spectroscopy-Chlorobenzyl Ethyl Ether by Dynamic NMR Spectroscopy

動的 NMR에 依한 $\alpha$-Chlorobenzyl Ethyl Ether의 이온解離速度에 關한 硏究

  • Chang-Yol Kim (Department of Science Education, Jeonbug National University)
  • 김창렬 (전북대학교 사범대학 화학교육과)
  • Published : 19800230

Abstract

Ionic dissociation rates of $\alpha$-chlorobenzyl ethyl ether in each solvent of toluene-$d_8$ and carbon tetrachloride were measured by the method of dynamic NMR spectroscopy. The spin system of these 1H NMR spectra was $AB_3$. The theoretical spectrum was calculated by computer simulation of dynamic NMR spectra, which agreed very well with observed spectra. From this computer simulation, the ionic dissociation rate constant k was obtained, and by Eyring plot with it, slope and intercept length was gained, from which kinetic parameters were calculated.The easiness of ionic dissociation depended upon solvent polarity. Activation enthalpy was 4.7 kcal/mole in toluene-$d_8$, 10.7 kcal/mole in carbon tetrachloride, and activation entropy was -35. 8 e.u. in toluene-$d_8$, -14.4 e.u. in carbon tetrachloride. It was understood that though the ${\Delta}H^{neq}$ value was small, this ionic dissociation had an easier procession in nonpolar solvents with increasing temperatures. Considering that the ionic dissociation could be thought as the first step of $S_N1$ mechanism, attention might be paid to the results that the value of ${\Delta}S^{neq}$ had a large negative value in comparison with a small ${\Delta}H^{neq}$.

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