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动态核磁共振(dynamic nuclear magnetic resonance,DNMR)是研究分子运动现象,获得活化参数的有力工具.有关酰胺类化合物的内旋转势垒已有多人用DNMR方法作过研究.本文用DNMR多重合并方法(multicoalescence)测得N,N-二甲基苯甲酰胺(DMB)及N,N-二乙基苯甲酰胺(DEB)绕C—N键旋转势垒的活化自由能△G~≠.为进一步讨论内旋转势垒的机制,除测量在不同溶剂中的活化参数外,还测定了在相应溶剂中的~(15)N化学位移δ_(16N).线性回归法计算表明,内旋转势垒的活化自由能△G~≠、~(15)N的化学位移δ_(16N)与溶剂性质参数E_T(30)有良好的线性关系.从不同温度下的谱图看出,随着温度升高,交换增快,出现谱线增宽、合并现象(图1).
Dynamic nuclear magnetic resonance (DNMR) is a powerful tool to study the phenomenon of molecular motion and obtain activation parameters.Numerical studies on the internal rotational barrier of amides have been performed by DNMR method.In this paper, The activation energy △ G ~ ≠ of the rotational barrier around C-N bond of N, N-dimethylbenzamide (DMB) and N, N-diethylbenzamide (DEB) measured by multicoalescence is In addition to measuring the activation parameters in different solvents, the chemical shift δ_ (16N) of ~ (15) N in the corresponding solvents was also discussed.The linear regression analysis showed that the internal rotation barrier The chemical shift δ_ (16N) of ~ (15) N has a good linear relationship with the solvent property parameter E_T (30) .From the spectra at different temperatures, with the increase of temperature , Exchange faster, spectral broadening, merger phenomenon (Figure 1).