利用IR光譜研究氫鍵的自異結合

Abstract

我們分別討論2-乙醯基吡咯在非極性或低極性溶劑中的氫鍵自異結合現象，透過不同系統更能了解我們新推導的公式實用程度以及自異結合系統的處理方式，我們可以由這些討論了解氫鍵的性質受到溫度、濃度和溶劑的影響程度。 探討氫鍵自異結合的現象有很多種方法，我們以FTIR為主要工具，NMR為輔助工具。利用2-乙醯基吡咯在稀薄溶液中氫鍵自異結合的氫鍵吸收光譜，分別求出單體與雙體的各別吸收度。觀測單、雙體吸收度隨濃度而變化的數據，代入我們推導出的二個新公式:單體公式 和雙體公式 ，分別求出單雙體吸收係數和自結合平衡常數K。把四種不同溫度下求得的平衡常數，以ln K對1/T作van't Hoff plot，可求得各個系統的標準結合焓 (△Ho)和標準結合熵 (△So)。兩條公式各別獨立，可以檢驗所得參數的一致性。另外討論到雙體的形式，根據公式判斷是屬於環狀雙體或是線性雙體，這樣可以更加了解化合物鍵結的形式。而在異結合系統部分，使用錯體公式 ，可以求出錯體的吸收係數 和平衡常數Kx 。

The hydrogen-bonded self-association of 2-acetylpyrrole in some nonpolar and slightly polar solvents at different temperatures has been studied, based on two newly derived equations, using IR spectroscopy with a help of NMR spectroscopy if it is necessary. The NH fundamental stretching exhibited by free monomer and associated dimer are identified and their integrated absorbances Am and Ad are used to fit the equations and respectively, to obtain the absorptivities of monomer (Em ) and that of dimer (Ed ), and the dimerization constant K; [B]o and b being initial solute concentration and optical path length. The Dimerization thus obtained at different temperatures are then employed to determine the enthalpy and entropy of dimerization by van’t Hoff plot. We also go a little bit further to study the heteroassociation of 2-acetylpyrrole with benzene in a nonpolar solvent CCl4 using the utility equation , where [X]o is the initial concentration of benzene and Ax is the integrated absorbance of complex AX and Kx is the hetero-association constant, to obtain Ex and Kx. In addition, the predominance of monomer-dimer equilibrium over monomer-oligomer equilibrium and the fact that the dimer is in the form of cyclic one are also throughly discussed.