以NMR測定自結合及自異結合平衡常數

Abstract

分子自身結合 關於分子內的氫鍵結合作用在NMR上的探討，前人多所研究，在此我們提出圖解法， 來處理分子自身結合的系統，選用的系統為 : 1-phenyl-3-pyrazolidinone溶在CDCl3， tropolone溶在CDCl3，caffeine溶在CDCl3，N-ethylacetamide溶在CDCl3， N-methylacetamide溶在CDCl3 ，2-hydroxyl-4-methyl-pyridine溶在CD3CN， 2-pyrrolidone溶在CD3CN中，等這七個系統。本圖解法有別於過去的方法，能精確地決 定單體位移，雙體位移與結合常數，並經由van't Hoff plot求出各系統之標準結合熵與 標準結合焓。 2. 自身結合與自異結合共存的系統 除了自身結合外，異分子結合的存在使得平衡現象更加複雜，傳統的 Benesi-Hildebrand(BH)法在使用上有所限制，考慮的作用僅有異分子結合，用來求 自異結合常數有顯著的偏差，迄今尚無有效的方法來求自異結合常數﹔我們提出一種 新的圖解方法，適用於兩種不同的分子自身結合，和一個分子自異結合共存的系統， 選用的系統為 :2-pyrrolidone(A)與2-hydroxyl-4-methyl-pyridinone(B)溶於CD3CN， 在決定自異結合常數上，獲得明顯的改善效果.圖解方法，適用於兩種不同的分子自 身結合，和一個分子自異結合共存的系統，選用的系統為 :2-pyrrolidone(A) 與2-hydroxyl-4-methyl-pyridinone(B)溶於CD3CN，在決定自異結合常數上，獲得 明顯的改善效果。

Self-association A graphic method for the simultaneous determination of the monomer shift, dimer shift and dimerization constant of a self-association system from the dilution NMR shift data is proposed. The method avoids the conventional extrapolation to infinite dilution to obtain the monomer shift. We have dealed with 7 systems: 1-phenyl-3-pyrazolidinone, tropolone, caffeine, N-ethylacetamide, N-methylacetamide in CDCl3, and 2-hydroxyl-4-methylpyridine, 2-pyrrolidone in CD3CN. 2. Coexistence of Self-association and Hetero-association Another novel graphic method to determine the Complex shift and equilibrium constant for a hetero-association, A+BAB, accompanying two self-associations: A+AA2, B+BB2 has been described. The method is to be used in conjunction with a previously proposed graphic determination of the monomer shift, dimer shift and dimerization constant. Our new method is advantageous over the conventional Benesi-Hildebrand (BH) plot in that the limitations (1) that the concentration of one component must be much less than that of the other and (2) that self- association of species is not allowed, are completely removed. The related parameters of the self-association of 2-pyrrolidone(A), 2-hydroxyl-4-methyl-pyridine(B) and the hetero-association of A with B in CD3CN has been used to demonstratehe use of the new graphic method.