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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，歡迎學(xué)習(xí)今天的課程有機(jī)波譜分析。繼續(xù)上一節(jié)課，我們?nèi)詫⒂懻?NMR 的基本原理。為了成功使用 NMR 作為分析工具，有必要了解這些方法基本的物理原理。核磁共振 化學(xué)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：許多元素同位素的核具有特征性的自旋量子數(shù)（I）。一些原子核具有整數(shù)自旋量子數(shù)（例如 I=1、2、3.），一些原子核具有分?jǐn)?shù)自旋量子數(shù)（例如 I=1/2、3/2、5/2.），而一些原子核則沒有自旋，I=0（例如12C，16O，32S 等）。自旋量子數(shù)（I）與原子核的質(zhì)量

4、（M）和原子數(shù)（Z）有關(guān) 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：只要質(zhì)量數(shù)和原子序數(shù)之一是奇數(shù)，I 就不為零 有機(jī)化學(xué)家特別感興趣的同位素是1H，13C，19F 和31P，它們的自旋數(shù)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：旋轉(zhuǎn)的帶電核產(chǎn)生磁場。在沒有外部磁場的情況下，樣品中核的磁矩是隨機(jī)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，當(dāng) NMR 磁性原子核受到強(qiáng)大的磁場（Bo）的作用時，它們傾向于使自旋方向與外部磁場（磁力線）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 的原子核具有球形電荷分布，其 NMR 行為最容易理解。其它自旋核具有非球形電荷分布，可以看成為扁長形或扁圓形的紡錘體。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個電四極矩，這使其譜圖太復(fù)雜而不用于結(jié)構(gòu)分析。P7:Magnetic Moment can be calculated according to this equation here.It is proportional to the spin number of a nuclear.P7：可以根據(jù)該公式計算磁矩。它與核的自旋數(shù)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：在量子力學(xué)中，原子核的核磁矩以 2I+1 的方式與外部施加的強(qiáng)度為 B0的磁場對齊，（自旋方向）既可以與 B0一致也可以與之相反。對于自旋核，有兩個可能的自旋方向。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：將樣品放在 NMR 儀中時，施加強(qiáng)磁場。自旋以 Lamour 頻率圍繞磁場旋轉(zhuǎn)，如果照

11、射具有與拉莫爾頻率匹配頻率的 RF 能量，進(jìn)動核將吸收能量，并且磁矩將激發(fā)至其高能態(tài)（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自旋態(tài)是 m=1/2 的低能態(tài)，自旋態(tài)是 m=-1/2 的高能態(tài)。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.(插入圖 12)P11：兩個相鄰能級之間的能量差以下方程式。其中 是旋磁比，它實(shí)際上測量原子核磁性的強(qiáng)度，并且對于每個原子核都是不同的，而 B0是施加的磁場強(qiáng)度。（插入圖 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 自選態(tài)之間的能量差取決于所施加的磁場（強(qiáng)度）。（通常小于 0.1 kcal/mol）。為了正確理解這一點(diǎn)，請回想一下之前的（學(xué)習(xí)內(nèi)容），紅外光譜能級躍遷為 1 至 10 kcal/mol，電子的躍遷要大 100 倍。因此，無線電波可以翻轉(zhuǎn)/激發(fā)原子核的自旋態(tài)。磁場，RF 射頻和核自旋態(tài)的相互作用是觀察 NMR 的關(guān)鍵！今天的課程就到這里。謝謝收看！