離子配對之NMR研究

Abstract

關於離子系統內氫鍵結合作用在NMR上探討，我們提出圖解法及應用Bromley 的公式1-2: logr±= -Am|Z+Z-|√Im/1+ai√Im+(0.06+0.6Bm|Z+Z-|Im)/[1+(1.5Im|Z+Z-|)]2+BmIm 其中 Am=e3/2.3026*(εkT)3/2*(2πρ0L./1000)1/2, Bm=(8πLe2ρ0/1000εkT)1/2 r± 為活性係數，Im為離子強度， ρ0為純溶劑密度， ε為溶劑介電係數， k為波玆曼常數， L為亞佛加厥數， e為電子電量的絕對值， Z為正負離子的電荷數， ai=1 在1:1的電解質中。選用的系統為： Methyl triphenyl-phosphonium bromide 溶在D20及 CD3SOCD3中， Benzyl triphenyl-phosphonium bromide, Benzyl triphenyl-phosphonium chloride溶在 CD3SOCD3中， (Bromomethyl) triphenyl-phosphonium bromide 溶在CD3SOCD3及DMF中。研究結果發現介電係數愈小，修正前與修正後的平衡常數偏差愈大，且濃度越 稀3 ，越能經由圖解法，求得更正確的平衡常數、單體位移及雙體位移，並經由van't Hoffplot求出各系統之標準結合熵及標準結合焓。

A graphic method for the simultaneous determination of teh monomer shift, dimer shift and dimerization constant of the ionpairing system from the dilution NMR shift data is proposed in conjunction with Bromley's equation. logr±= -Am|Z+Z-|√Im/1+ai√Im+(0.06+0.6Bm|Z+Z-|Im)/[1+(1.5Im|Z+Z-|)]2+BmIm where Am=e3/2.3026*(εkT)3/2*(2πρ0L./1000)1/2, Bm=(8πLe2ρ0/1000εkT)1/2 r± is activity coefficient, Im ion strength, ρ0 density of solvent, ε dielectric constant of the solvent, k Boltzmann constant, L Avogadro's number, e the absolute value of electronic charge, Z valence, ai=1 in case of 1:1 aqueous electrolyte solutions. We deal with six systems: Methyl triphenyl-phosphonium bromide in D20 and CD3SOCD3, Benzyl triphenyl-phosphonium bromide, Benzyl triphenyl-phosphonium chloride in CD3SOCD3, (Bromomethyl) triphenyl-phosphonium bromide in CD3SOCD3 and DMF. If the value of dielectric constant is small, the improvement from the no-modified to the modified dimerization constants is appreciable. As the concetrations were diluted, the more precise value of teh monomer shifts, dimer shifts and dimerization constants are obtained. Standard enthalpies and entropies of self-association were also obtained by van't Hoff plots.