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1、P1:Hello everyone,welcome to todays class-Organic Spectroscopic Analysis.To continue the previous class,we will still talk about the physical principles of NMR spectroscopy.To be successful in using NMR as an analytical tool,it is necessary to understand the physical principles on which the methods
2、are based.Nuclear Magnetic Resonance Chemical Shift Spin-spin Coupling P1：大家好，欢迎学习今天的课程有机波谱分析。继续上一节课，我们仍将讨论 NMR 的基本原理。为了成功使用 NMR 作为分析工具，有必要了解这些方法基本的物理原理。核磁共振 化学位移 自旋耦合 P2:The nuclei of many elemental isotopes have a characteristic spin number(I).Some nuclei have integral spins(e.g.I=1,2,3.),some hav
3、e fractional spins(e.g.I=1/2,3/2,5/2.),and a few have no spin,I=0(e.g.12C,16O,32S,.).The spin number(I)is related to the mass(M)and atomic number(Z)of the nucleus P2：许多元素同位素的核具有特征性的自旋量子数（I）。一些原子核具有整数自旋量子数（例如 I=1、2、3.），一些原子核具有分数自旋量子数（例如 I=1/2、3/2、5/2.），而一些原子核则没有自旋，I=0（例如12C，16O，32S 等）。自旋量子数（I）与原子核的质量
4、（M）和原子数（Z）有关 P3:As long as one of the mass number and atomic number is odd,I is not zero Isotopes of particular interest to organic chemists are 1H,13C,19F(Fluorine)and 31P(phosphorus),all of which have spin number I=1/2.P3：只要质量数和原子序数之一是奇数，I 就不为零 有机化学家特别感兴趣的同位素是1H，13C，19F 和31P，它们的自旋数I=1/2。P4:The spi
5、nning charged nucleus generates a magnetic field.In the absence of external magnetic field,the magnetic moments of the nuclei in a sample are randomly oriented.P4：旋转的带电核产生磁场。在没有外部磁场的情况下，样品中核的磁矩是随机取向的。P5:However,when NMR active nuclei are subjected to a powerful magnetic field(Bo),they have a tendenc
6、y to align their spins with the external field P5：但是，当 NMR 磁性原子核受到强大的磁场（Bo）的作用时，它们倾向于使自旋方向与外部磁场（磁力线）一致或相反 P6:Spin 1/2 nuclei have a spherical charge distribution,and their NMR behavior is the easiest to understand.Other spin nuclei have nonspherical charge distributions and may be analyzed as prolat
7、e or oblate spinning bodies.All nuclei with non-zero spins have magnetic moments().But the nonspherical nuclei also have an electric quadrupole moment,which makes it too complicated to be of use for structure analysis.P6：自旋 1/2 的原子核具有球形电荷分布，其 NMR 行为最容易理解。其它自旋核具有非球形电荷分布，可以看成为扁长形或扁圆形的纺锤体。具有非零自旋的所有核都具有
8、磁矩（）。但是非球形原子核也有一个电四极矩，这使其谱图太复杂而不用于结构分析。P7:Magnetic Moment can be calculated according to this equation here.It is proportional to the spin number of a nuclear.P7：可以根据该公式计算磁矩。它与核的自旋数成正比。P8:In quantum mechanical terms,the nuclear magnetic moment of a nucleus can align with an externally applied magnet
9、ic field of strength Bo in 2I+1 ways,either with or against the applied field Bo.For a spin nucleus,two orientations are possible P8：在量子力学中，原子核的核磁矩以 2I+1 的方式与外部施加的强度为 B0的磁场对齐，（自旋方向）既可以与 B0一致也可以与之相反。对于自旋核，有两个可能的自旋方向。P9:When the sample is placed in an NMR spectrometer,a strong magnetic field is applie
10、d.The spins precess around the applied field at the Lamour frequency If RF energy having a frequency matching the Larmor frequency is introduced,the precessing nucleus will absorb energy and the magnetic moment will flip to its high energy state(I=-1/2).P9：将样品放在 NMR 仪中时，施加强磁场。自旋以 Lamour 频率围绕磁场旋转，如果照
11、射具有与拉莫尔频率匹配频率的 RF 能量，进动核将吸收能量，并且磁矩将激发至其高能态（I=-1/2）。P10:State is the lower energy state with m=1/2 and state is the higher energy state with m=-1/2.P10自旋态是 m=1/2 的低能态，自旋态是 m=-1/2 的高能态。P11:Energy separation between two adjacent levels is expressed as the following equation here.Where is the gyromagnet
12、ic ratio,which essentially measures the strength of the nuclear magnets and is different for each nucleus,and B0 is the strength of the applied magnetic field.(插入图 12)P11：两个相邻能级之间的能量差以下方程式。其中 是旋磁比，它实际上测量原子核磁性的强度，并且对于每个原子核都是不同的，而 B0是施加的磁场强度。（插入图 12）P13：The difference in energy between the and states
13、depends on the applied field.(Typically less than 0.1 kcal/mol).To put this in perspective,recall that infrared transitions involve 1 to 10 kcal/mole and electronic transitions are nearly 100 time bigger.Radiowaves can thus flip/excite spin states of atomic nuclei.It is the interplay of magnetic fie
14、ld,RF waves and nuclear spin states that is the key to observing NMR！So that is it for todays lecture.Thank you for watching.P13：和 自选态之间的能量差取决于所施加的磁场（强度）。（通常小于 0.1 kcal/mol）。为了正确理解这一点，请回想一下之前的（学习内容），红外光谱能级跃迁为 1 至 10 kcal/mol，电子的跃迁要大 100 倍。因此，无线电波可以翻转/激发原子核的自旋态。磁场，RF 射频和核自旋态的相互作用是观察 NMR 的关键！今天的课程就到这里。谢谢收看！