醇与极性有机溶剂间氢键的多核NMR研究

MULTI-NUCLEAR NMR STUDIES OF HYDROGEN BONDING BETWEEN ALCOHOLS AND APROTIC SOLVENTS

醇是一类重要的有机溶剂,对其结构和性质的研究已有很长历史。由于OH的存在,醇分子间存在着较强的氢键缔合作用,使其结构变得复杂,因而较难对它得到一个很清楚的认识。用NMR方法研究氢键也有几十年历史。早在五十年代,Arnold,Becker等就用~1HNMR研究了EtOH在CCl_4中的行为,测量了化学位移随浓度的变化。Becker认为当醇浓度很稀时,体系中只存在单体-二聚体平衡,井结合IR数据求得了平衡常数及缔合物位移。

Binary systems of alcohols and aprotic solvents have been studied systematicallyby NMR measurements. ~1H, ^(13)C, ^(15)N and ^(17)O chemical shifts and proton T_1 have beenmeasured. The effects of solvents on ~1H and ^(13)C chemical shifts of alcohols were discussed. ^(13)C chemical shifts of α-carbon atom of alcohol were used to determine theability of solvents to distort or disrupt the structure of alcohol, while their ~1H che-mical shifts were used to measure the strength of hydrogen bond between solventsand alcohols. The result was obtained showing that the stronger the solvent as a do-nor, the stronger its ability to disrupt the structure of alcohols. Chemical shifts of solvents have also been measured. It was thought that theirvariation was directly connected with hydrogen bonding between solvents and alcoholsIn accordance with the equilibria in systems, chemical shifts of solvents were simula-ted and the equilibrium constants and chemical shifts of hydrogen-bonded complexeswere obtained. Relationship between chemical shifts of alcohols unbonded with solv-ents and their concentration has been obtained. The proportion of free OH protons inalcohols was thus quantitatively described