NMR补充说明.ppt

磁核和自旋量子数 磁核和自旋量子数 第1类：质子数和中子数均为偶数，质量数为偶数 磁核和自旋量子数 第2类：质子数和中子数均为奇数，质量数为偶数 磁核和自旋量子数 第3类：质子数和中子数其中一个为奇数，质量数为奇数 磁核和自旋量子数 磁核和自旋量子数 原子核的自旋角动量 原子核的总角动量来自于以下几个方面：质子的轨道角动量和自旋角动量，中子的轨道角动量和自旋角动量。 以上4个角动量耦合成原子核的总角动量。会有多个可能值。 乙醇的NMR谱图 乙醇的NMR谱图 Context When a trace amount of acid is added to the ethanol, the spectrum changes as shown in Fig. 1.4. The lack of multiplicity of the hydroxyl proton signal is due to rapid exchange of hydroxyl protons, which is catalyzed by acid. As a result of this exchange any one hydroxyl proton, during a certain interval of time, is attached to a number of different ethanol molecules and thus experiences all possible spin arrangements of the methylene group. If the chemical exchange occurs with a frequency which is substantially greater than the frequency separation of the components of the multiplet from the hydroxyl proton signal, the magnetic effects corresponding to the three possible spin arrangements of the methylene protons are averaged out, and a single sharp absorption line is observed for the hydroxyl proton. In other words, rapid exchange causes spin decoupling between the hydroxyl and methylene protons. The quartet splitting of the methylene proton signal remains after the rapid exchange due to the spin coupling with methyl protons. 《材料近代分析测试方法》插图 ChemDraw预测结果 网络数据库查询结果 氢键使醇羟基氢化学位移存在差别 The more concentrated the solution, the more molecules can come into contact with each other and hydrogen bond. At high dilution (no H bonding), hydroxyl protons absorb near 0.5–1.0 ppm; in concentrated solution, their absorption is closer to 4–5 ppm. * [A Complete Introduction to NMR Spectroscopy, p. 8] [A Complete Introduction to NMR Spectroscopy, p. 8] [A Complete Introduction to NMR Spectroscopy, p. 8] [NMR of Polymers, pp. 3-4] [NMR Spectroscopy of Polymers, p. 3] [NMR Spectroscopy of Polymers, pp. 68] [NMR Spectroscopy of Polymers, pp. 68] [材料近代分析测试方法，pp. 186-187] http://riodb.ibase.aist.go.jp/ [Introduction to Spectroscopy, 4th Edition] *