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1、P1:Hello everyone,welcome to todays class-Organic Spectroscopic Analysis.In the previous lecture,we have learned about the principles of NMR.Lets recall how to produce NMR phenomena.1.Firstly,the spin number of nuclei is not zero.There is an external magnetic field B0.Radio frequency electromagnetic
2、 waves in the vertical direction of B0.2.When the frequency of the radio frequency electromagnetic wave is the same as the Larmor frequency of the spin nucleus,the nucleus absorbs the energy of the radio frequency wave and transitions from the low energy state to the high energy state,that is,nuclea
3、r magnetic resonance occurs.P1：大家好，欢迎学习今天的课程有机波谱分析。在上一课中，我们了解了 NMR 原理。让我们回想一下如何产生 NMR现象。1.首先，原子核的自旋量子数不为零。有一个外加磁场 B0，B0垂直方向发射射频电磁波。2.当射频电磁波的频率与自旋核的拉莫尔频率相同时，原子核吸收射频波的能量并从低能态转变为高能态，即核能发生磁共振。P2:An NMR machine consists of:(1)A powerful,supercooled magnet(which is stable with sensitive control,producing
4、a precise magnetic field).(2)A radio-frequency transmitter(emitting a very precise frequency).(3)A detector to measure the emission of radio frequency by the sample.(4)A recorder(to plot the output).P2：NMR 机器包括：（1）强大的超冷磁体（稳定，可以灵敏的控制，产生精确的磁场）。（2）射频发射器（发射非常精确的频率）。（3）检测器，用于测量样品发射的频率。（4）记录器（绘制输出）。P5:Mag
5、net The NMR magnet is one of the most expensive components of the nuclear magnetic resonance spectrometer system.Most magnets are of the superconducting type.The NMR magnet is one of superconducting type and has to be immersed in liquid helium.It is the most expensive component The following image i
6、s an actual cut-away view of a superconducting magnet.Going from the outside of the magnet to the inside,we see a vacuum region followed by a liquid nitrogen reservoir.The vacuum region is filled with several layers of a reflective mylar mal.The function of the mylar is to reflect thermal photons,an
7、d thus diminish heat from entering the magnet.Within the inside wall of the liquid nitrogen reservoir,we see another vacuum filled with some reflective mylar.The liquid helium reservoir comes next.This reservoir houses the superconducting coil of wire.P5：NMR 磁体是核磁共振光谱仪系统中最昂贵的组件之一。大多数磁体是超导类型的。NMR 磁体是
8、超导类型的，必须浸入液态氦中。它是最昂贵的组件 下图是超导磁体的实际剖视图。从磁体的外部到内部，我们看到了一个真空区域，后面是一个液氮储存器。真空区域充满了多层反射性聚酯薄膜。聚酯薄膜的功能是反射热光子，从而减少热量进入磁体。在液氮储存器的内壁内，我们看到另一个真空，里面充满了一些反射性聚酯薄膜。接下来是液氦储存器。该储存器容纳导线的超导线圈。P6:Why should the proton nuclei behave differently in the NMR experiment?The answer to this question lies with the electron(s)s
9、urrounding the proton：Since electrons are charged particles,they move in response to the external magnetic field so as to generate a secondary field that opposes the much stronger applied field.This secondary field shields the nucleus from the applied field P6：为什么核磁共振中质子的行为不同？这个问题的答案取决于质子周围的电子：由于电子是
10、带电粒子，因此它们会响应于外部磁场而运动，从而生成与外加强磁场相对的感应磁场。这个感应磁场屏蔽了原子核。P7:The electron density around each nucleus in a molecule varies according to the types of nuclei and the bonds in the molecule.The opposing field and therefore the effective field at each nucleus will vary.This is called the chemical shift phenome
11、non.P7：分子中每个原子核周围的电子密度根据原子核的类型和分子中的化学键而变化。每个核的屏蔽磁场以及有效场将有所不同，这个现象称为化学位移。P8：:The external field(B0)must be increased to compensate for the induced shielding field.As a consequence,the NMR equation need be modified to this format:0=B0(1-)/2,where is the shielding tensor.The 0(Larmor frequency)of the p
12、rotons in the electron rich chemical environments,has bigger B0.When 0 is unchanged,change B0(called sweep field),the nuclei of different environments in the molecule will have different resonance absorption peaks due to different.P8：B0）必须增加以补偿感应的屏蔽场。NMR 方程修改为以下形成：0=B0(1-)/2,其中是屏蔽常数。0（Larmor 频率）具有更大
13、的 B0。0不变时，改变 B0（称为扫场），由于的不同，分子中不同环境的核将具有不同的共振吸收峰。改变 B0（称为扫场），分子中不同的原子核会因环境不同而出现不同共振吸收峰。P9:Consider the methanol molecule.The resonance frequency of two types of nuclei in this example differ.This difference will depend on the strength of the applied magnetic field,B0.The greater the value of B0,the
14、greater the frequency difference.This relationship could make it difficult to compare NMR spectra taken on spectrometers operating at different field strengths.The term chemical shift was developed to avoid this problem.P9：以甲醇分子为例，两种类型的氢核的共振频率不同。这种差异将取决于施加的磁场强度 B0。B0的值越大，频率差越大。这样可能使比较在不同场强下运行的光谱仪上获得
15、的 NMR 光谱变得困难。为避免此问题，定义了化学位移。P11:Chemical shift is expressed as the following equation.The location of an NMR signal in a spectrum is to be reported relative to a reference signal from a standard compound added to the sample.P11：化学位移用以下方程式表示，NMR 谱图种信号的位置表示为添加到样品中的标准化合物峰的相对信号。P12:Such a reference stan
16、dard should be chemically unreactive,and easily removed from the sample after the measurement.Also,it should give a single sharp NMR signal that does not interfere with the resonances normally observed for organic compounds.Tetramethylsilane,(CH3)4Si,usually referred to as TMS,meets all these charac
17、teristics,12H and 4C suffer the same chemical enviroment and has become the reference compound of choice for 1H and 13C NMR.So todays lecture,we have learned about the NMR instrument and chemical shift.Lets continue to learn more about NMR in the following lectures.Thank you for watching!P12：内标应化学反应惰性，并在测量后易于从样品中去除。同样，它应给出单个清晰的 NMR 信号，该信号不会干扰通常观察到的有机化合物的共振峰。四甲基硅烷（CH3）4Si，通常称为 TMS，满足所有这些特征，12H 和4C 具有相同的化学环境，并已成为 1H 和 13C NMR 的内标。因此，在今天的课程中，我们了解了 NMR 仪和化学位移。在接下来的课程中，我们将继续学习有关 NMR 的更多信息。感谢收看！