大二有機(jī)第九章

1、1. Where might the following compound have IR absorption?ReviewExercise:IR(KBr) 3310(s), 3030(s) 2940 (s), 2860 (s) 2130 (m) 1610(w), 1490(m) 630(s) (cm-1) : stretchstretchstretch stretchstretch bending3500 cm-1OH stretchChapter Eight Infrared Spectroscopy and Nuclear Magnetic Resonance Spectroscopy

2、Infrared Spectra of Hydrocarbons and Some CommonFunctional GroupsInterpreting(解析) Infrared SpectraThe Nature of NMR AbsorptionsNuclear Magnetic Resonance SpectroscopyChemical Shifts1H NMR SpectroscopyIntroduction of Structure Determination Electromagnetic RadiationInfrared Spectroscopy of Organic Mo

3、leculesNuclear Magnetic Resonance Spectroscopy Nuclear Magnetic Resonance (NMR) Spectroscopy is the most valuable spectroscopic technique available to organic chemists. 1952年Nobel prize for physics the physics experiment that revolutionized chemistry Felix BlochEdward PurcellI = : 1H, 13C, 31P, 29Si

4、Nuclear Magnetic Resonance SpectroscopyAbsence of an external magnetic field-Orientedrandomly.Applied external magnetic fieldspecific orientations (paralleled to, or antiparalleled to).Nuclear Magnetic Resonance Spectroscopysampleirradiated energy absorptionElectromagnetic radiation lower-energy sta

5、te “spin-flips”(躍遷) to the higher-energy state. When this spin-flip occurs, the magnetic nuclei are said to be in resonance (共振) with the applied radiation，hence the name nuclear magnetic resonance (核磁共振).E1E2EBO= 0EBO=14,100 GBO=23,500 GEE = rhBo/2external magnetic fieldThe operation of a basic NMR

6、 spectrometer is illustrated as below.The Nature of NMR Absorptions An organic sample is dissolved in a suitable solvent (usually Deuterichloroform (氘代氯仿), CDCl3, which has no hydrogen) and placed in a thin glass tube between the poles of a magnet.The instrument of 500M 1HNMR is shown below:The Natu

7、re of NMR AbsorptionsNuclear Magnetic Resonance SpectroscopyE = rhBo/2=h = rBo/2 You might expect all 1H nucleus in a molecule to absorb energy at the same frequency. If this were true, we would observe only a single NMR absorption band in the 1H spectrum of a molecule,absorption frequency is not th

8、e same for all 1H Why?Chapter Eight Infrared Spectroscopy and Nuclear Magnetic Resonance SpectroscopyInfrared Spectra of Hydrocarbons and Some CommonFunctional GroupsInterpreting(解析) Infrared SpectraThe Nature of NMR AbsorptionsNuclear Magnetic Resonance SpectroscopyChemical Shifts1H NMR Spectroscop

9、yIntroduction of Structure Determination Electromagnetic RadiationInfrared Spectroscopy of Organic MoleculesThe Nature of NMR AbsorptionsAll nuclei in molecules are surrounded by electronsthe electrons moving around nucleiset up tiny local magnetic fieldsact in opposition to the applied fieldBeffect

10、ive = Bapplied - Blocal感應(yīng)磁場(chǎng) In describing this effect of local fields(感應(yīng)磁場(chǎng)), we say that nuclei are shielded(屏蔽) from the full effect of the applied field by the surrounding electrons. Since each specific nucleus in a molecule is in a slightly different electronic environment, each nucleus is shield

11、ed to a slightly different extent and the effective magnetic field felt by each is not the same.The Nature of NMR Absorptions 不同化學(xué)環(huán)境的氫核，受到不同程度的屏蔽效應(yīng)，因而在NMR的不同位置上出現(xiàn)吸收峰，這種位置上的差異成為化學(xué)位移。 Chapter Eight Infrared Spectroscopy and Nuclear Magnetic Resonance SpectroscopyInfrared Spectra of Hydrocarbons and So

12、me CommonFunctional GroupsInterpreting(解析) Infrared SpectraThe Nature of NMR AbsorptionsNuclear Magnetic Resonance SpectroscopyChemical Shifts1H NMR SpectroscopyIntroduction of Structure Determination Electromagnetic RadiationInfrared Spectroscopy of Organic MoleculesThe Nature of NMR AbsorptionsFor

13、 example, the 1H spectrum of ethyl acetate is shown as below:Chemical ShiftsChemical shift () ： The position on the chart at which a nucleus absorbs is called its chemical shift. 化學(xué)位移, ppm=(樣品TMS)106/ o ppm: part per million(百萬分之一) To define the position of an absorption, the NMR chart is calibrated

14、 (內(nèi)標(biāo)) and a reference point is used. the chemical shift of TMS is set as the zero point.TMS：Tetramethyl silicane 四甲基硅烷Chemical Shifts NMR spectra are displayed on charts that show the applied field strength increasing from left to right. Thus the left part of the chart is the low-field, or the downf

15、ield side, and the right part is the high-field, or upfield side. 零點(diǎn)-1-2-312345678910:TMSDownfield 低場(chǎng)Upfield 高場(chǎng) We said previously that differences in chemical shifts are caused by the small local magnetic fields of electrons surrounding the nuclei. Nuclei that are more strongly shielded need a high

16、er applied field to bring them into resonance and therefore absorb on the right side of the NMR chart.Chemical ShiftsChapter Eight Infrared Spectroscopy and Nuclear Magnetic Resonance SpectroscopyInfrared Spectra of Hydrocarbons and Some CommonFunctional GroupsInterpreting(解析) Infrared SpectraThe Na

17、ture of NMR AbsorptionsNuclear Magnetic Resonance SpectroscopyChemical Shifts1H NMR SpectroscopyIntroduction of Structure Determination Electromagnetic RadiationInfrared Spectroscopy of Organic Molecules1H NMR Spectroscopy1. Factors affecting the chemical shift (1). The effect of electronegativity (

18、電負(fù)性)electronegativity is strongerthe electron density around the nuclei is lowernuclei are less strongly shieldedchemical shift move to the lower field1H NMR SpectroscopyHH1H NMR SpectroscopyBut in fact:Why ?and:(2) Magnetic anisotropy effect (磁各向異性效應(yīng))1H NMR SpectroscopyB0local magnetic fields paral

19、leled to the applied external magnetic fieldlocal magnetic fields anti paralleled to the applied external magnetic field = 4.55.7 ppm= 23 ppm 構(gòu)成化學(xué)鍵的電子，在外加磁場(chǎng)作用下，產(chǎn)生一個(gè)各向異性的磁場(chǎng)。使處于化學(xué)鍵不同空間位置上的質(zhì)子受到不同的屏蔽作用-即磁各向異性。 1H NMR SpectroscopyB0B0= 9.410 ppm = 4.55.7 ppmB0 = 4.55.7 ppm = 6.09.0 ppm1H NMR Spectroscopy

20、HH1H NMR SpectroscopyThe absorption of a proton splits into multiple peaks a multiplet.three peaks (a triplet) 三重峰four peaks (a quartet) 四重峰Called spin-spin splitting(自旋偶合), the phenomenon of multiple absorptions is caused by the interaction, or coupling of the spins of nearby nuclei.多重峰Coupling is

21、a reciprocal(相互的) interaction between two adjacent groups of protons.1H NMR SpectroscopyBO1H NMR singnal of HaThe local magnetic fields produced by HbHb 的磁矩將Ha的核磁信號(hào)分裂成強(qiáng)度相同的二重峰BO1H NMR SpectroscopyNumber of equivalent Type of multiplet Ratio of adjacent protons observed intensities 0 Singlet (單峰) 1 1

22、 Doublet (二重峰) 1:1 2 Triplet (三重峰) 1:2:1 3 Quartet (四重峰) 1:3:3:1 1H NMR SpectroscopyThe signal of a proton that has n equivalent neighboring protons is split into a multiplet of n+1 peaks.1H NMR Spectroscopy The distance between peaks in a multiplet is called the coupling constant (偶合常數(shù)), denoted J.

23、nJabcoupling constant (Hz)1H NMR(CDCl3) : 1.18 (3H, s, CH3), 6.38 (1H, m, Ar-H), 4.91 (2H, d, CH2)The format of 1H NMR data in thesis:S-單峰，d-雙峰，t-三重峰，q-四重峰，m-多重峰3JHH = 7.5 Hz1H NMR SpectroscopyNo splitting occursSplitting occurs 分子中一組核，化學(xué)位移相同，且對(duì)組外任一核的偶合常數(shù)也都相同。則這組核稱為磁等同核 磁等同核之間的偶合作用不產(chǎn)生峰的分裂，只有磁不等同核之間的

24、偶合才會(huì)產(chǎn)生峰的分裂。2. Interpreting (解析) 1H NMR spectroscopy1H NMR Spectroscopy1H NMR spectroscopy can give us the following information: 1. 吸收峰的組數(shù)-有幾類不同的H核； 2. 峰的面積（積分強(qiáng)度）-每類H的相對(duì)數(shù)目； 3. 峰的裂分?jǐn)?shù)目-鄰位等性H核的數(shù)目； 4. 峰的位置（值）-各類型H所處的化學(xué)環(huán)境； 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0Chemical shift (, ppm)4.13.3CH3OCH2CN10mmH1:H22:315mm1H NMR Spectroscopy1H NMR Spectroscopy1. Predict the pattern of the following compounds:one singletone triplet + one quartet + one doubletone singlet + one singlet one triplet + one triplet + one singletone singletone quartet + one doubletone singlet + one singlet one doub