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Journal of the Korean Chemical Society (JKCS)

ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 24, Number 1
JKCSEZ 24(1)
February 20, 1980 

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

동적 NMR에 의한 α-Chlorobenzyl Ethyl Ether의 이온해리속도에 관한 연구
Chang-Yol Kim

동적 핵자기공명법에 대하여 toluene-d8 및 carbon tetrachloride 용매속에서의 α-chlorobenzyl ethyl ether의 이온해리속도를 측정하였다. 먼저, 동적NMR spectra를 얻고 JAB, T2, ΔvAB 값 등을 이용하여 computer simulation에 의한 이론spectra를 얻었는데 실측spectra와 매우 잘 일치하였으며, 이로부터 해리속도정수 k를 얻고 이 k의 Eyring plot에 의하여 기울기와 절편의 길이를 알고 이로부터 동력학적 parameter를 얻었다. 이온 해리의 난역도는 용매의 극성에 의존하였으며 활성화 enthalpy는 toluene-d8 용매중에서 4.7kcal/mole 이었고 carbon tetrachloride 용매중에서 10.7kcal/mole 이었다. 활성화 entropy는 toluene-d8 용매중에서 -35.8 e.u. 이었고 carbon tetrachloride 용매중에서 -14.4 e.u. 이었다. Sn1 mechanism의 초기단계로 볼 수 있는 이 이온 해리는 ΔH≠ 값이 작아도 비극성 비양자성용매중에서 이온해리가 용역함을 알았으며 작은 ΔH≠에 비하여 ΔS≠는 음의 큰 값을 가졌음은 주목할 필요가 있다.

Ionic dissociation rates of α-chlorobenzyl ethyl ether in each solvent of toluene-d8 and carbon tetrachloride were measured by the method of dynamic NMR spectroscopy. The spin system of these 1H NMR spectra was ABX3. 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-d8, 10.7 kcal/mole in carbon tetrachloride, and activation entropy was -35. 8 e.u. in toluene-d8, -14.4 e.u. in carbon tetrachloride. It was understood that though the ΔH≠ 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 SN1 mechanism, attention might be paid to the results that the value of ΔS≠ had a large negative value in comparison with a small ΔH≠.

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