NMR Determination of Hydrogen Bond Thermodynamics in a Simple Diamide: A Physical Chemistry Experiment
NMR Determination of Hydrogen Bond Thermodynamics in a Simple Diamide: A Physical Chemistry Experiment
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简单二酰胺中氢键热力学的 NMR 测定：物理化学实验
DOI：
10.1021/ed400644a
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发表时间：
2015
影响因子：
3
通讯作者：
M. Schofield
中科院分区：
文献类型：
--
作者：
J. Morton;C. Joe;M. C. Stolla;Sophia R. Koshland;C. Londergan;M. Schofield
变温核磁共振谱用于测定简单二酰胺中氢键形成的ΔH°和ΔS°。在这个为期两三天的实验中，学生将从甲胺和相应的二酯合成N，N′-二甲基丙二酰胺、二甲基琥珀酰胺、二甲基戊二酰胺或二甲基己二酰胺（通常重结晶产率为50%），并在200至313 K之间的温度下记录NMR光谱。制备浓度为1.00 mM-13.1 M（纯品）的N-甲基乙酰胺溶液，记录其NMR光谱，以测定酰胺质子在氢键（δB）和非氢键（δN）限度内的化学位移。利用这些数据，确定了开链二酰胺转化为具有分子内氢键的环状结构的平衡常数ΔH°和ΔS°。
Variable temperature NMR spectroscopy is used to determine the ΔH° and ΔS° of hydrogen bond formation in a simple diamide. In this two- or three-day experiment, students synthesize N,N′-dimethylmalonamide, dimethylsuccinamide, dimethylglutaramide, or dimethyladipamide from methylamine and the corresponding diester (typically in 50% recrystallized yield) and record NMR spectra at temperatures between 200 and 313 K. Solutions of N-methylacetamide in concentrations between 1.00 mM and 13.1 M (neat) are prepared and their NMR spectra recorded to determine the chemical shift of the amide proton in the hydrogen-bonded (δB) and nonbonded (δN) limits. By using these data, the equilibrium constants, ΔH°, and ΔS° for the conversion of an open-chain diamide to a cyclic structure with an intramolecular hydrogen bond are determined.