有機(jī)化學(xué)：第九章-2Eight Infrared Spectroscopy and Nuclear

1、1. Where might the following compound have IR absorption?ReviewExercise:CH2CH2CH2CCHIR(KBr) 3310(s), 3030(s) 2940 (s), 2860 (s) 2130 (m) 1610(w), 1490(m) 630(s) (cm-1) : CHstretchArHstretchCH2stretchCC stretchAr (C=C)stretchCH bending3500 cm-1OH stretchChapter Eight Infrared Spectroscopy and Nuclear

2、 Magnetic Resonance SpectroscopyInfrared Spectra of Hydrocarbons and Some CommonFunctional GroupsInterpreting(解析解析) Infrared SpectraThe Nature of NMR AbsorptionsNuclear Magnetic Resonance SpectroscopyChemical Shifts1H NMR SpectroscopyIntroduction of Structure Determination Electromagnetic RadiationI

3、nfrared Spectroscopy of Organic MoleculesNuclear Magnetic Resonance Spectroscopy Nuclear Magnetic Resonance (NMR) Spectroscopy is the most valuable spectroscopic technique available to organic chemists. 1952年年Nobel prize for physics the physics experiment that revolutionized chemistry Felix BlochEdw

4、ard PurcellI = : : 1H, 13C, 31P, 29SiNuclear Magnetic Resonance SpectroscopyAbsence of an external magnetic field- Orientedrandomly.Applied external magnetic fieldspecific orientations (paralleled to, or antiparalleled to).Nuclear Magnetic Resonance Spectroscopysampleirradiated energy absorptionElec

5、tromagnetic radiation lower-energy state “spin-flips”(躍遷躍遷) to the higher-energy state. When this spin-flip occurs, the magnetic nuclei are said to be in resonance (共振共振) with the applied radiation，hence the name nuclear magnetic resonance (核磁共振核磁共振).E1E2EBO= 0EBO=14,100 G BO=23,500 GEE = rhBo/2exte

6、rnal magnetic fieldThe operation of a basic NMR spectrometer is illustrated as below.The Nature of NMR Absorptions An organic sample is dissolved in a suitable solvent (usually Deuterichloroform (氘代氯仿氘代氯仿), CDCl3, which has no hydrogen) and placed in a thin glass tube between the poles of a magnet.T

7、he instrument of 500M 1HNMR is shown below:The Nature 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 sp

8、ectrum of a molecule,absorption frequency is not the same for all 1H Why?C4H8O2HHHCH3COCH2CH3OChapter Eight Infrared Spectroscopy and Nuclear Magnetic Resonance SpectroscopyInfrared Spectra of Hydrocarbons and Some CommonFunctional GroupsInterpreting(解析解析) Infrared SpectraThe Nature of NMR Absorptio

9、nsNuclear Magnetic Resonance SpectroscopyChemical Shifts1H NMR SpectroscopyIntroduction of Structure Determination Electromagnetic RadiationInfrared Spectroscopy of Organic MoleculesThe Nature of NMR AbsorptionsAll nuclei in molecules are surrounded by electronsthe electrons moving around nucleiset

10、up tiny local magnetic fieldsact in opposition to the applied fieldBeffective = Bapplied - Blocal感應(yīng)磁場感應(yīng)磁場 In describing this effect of local fields( (感應(yīng)磁場感應(yīng)磁場),), we say that nuclei are shielded(屏蔽屏蔽) from the full effect of the applied field by the surrounding electrons. Since each specific nucleus

11、 in a molecule is in a slightly different electronic environment, each nucleus is shielded 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)，因而在的屏蔽效應(yīng)，因而在NMR的不同位置的不同位置上出現(xiàn)吸收峰，這種位置上的差異成上出現(xiàn)吸收峰，

12、這種位置上的差異成為為化學(xué)位移?；瘜W(xué)位移。 Chapter Eight Infrared Spectroscopy and Nuclear Magnetic Resonance SpectroscopyInfrared Spectra of Hydrocarbons and Some CommonFunctional GroupsInterpreting(解析解析) Infrared SpectraThe Nature of NMR AbsorptionsNuclear Magnetic Resonance SpectroscopyChemical Shifts1H NMR Spectrosc

13、opyIntroduction of Structure Determination Electromagnetic RadiationInfrared Spectroscopy of Organic MoleculesC4H8O2HHHCH3COCH2CH3OThe Nature of NMR AbsorptionsFor example, the 1H spectrum of ethyl acetate is shown as below:Chemical ShiftsChemical shift () ： The position on the chart at which a nucl

14、eus absorbs is called its chemical shift. 化學(xué)位移化學(xué)位移, ppm=(樣品樣品TMS) )106/ o ppm: part per million( (百萬分之一百萬分之一) ) To define the position of an absorption, the NMR chart is calibrated (內(nèi)標(biāo)內(nèi)標(biāo)) and a reference point is used. SiCH3H3CCH3CH3the chemical shift of TMS is set as the zero point.TMS：Tetramethyl

15、silicane 四甲基硅烷四甲基硅烷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 downfield side, and the right part is the high-field, or upfield side. 零點零點-1-2-312345678910 :TMSDownfie

16、ld 低場低場Upfield 高場高場 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 higher applied field to bring them into resonance and therefore absorb on the right side of the

17、NMR chart.Type of proton chemical shift( d, ppm)Type of proton chemical shift( d, ppm)1oAlkyl RCH30.8-1.02oAlkyl RCH2R1.2-1.43oAlkyl R3CH1.4-1.7RCH31.6-1.9ArCH32.2-2.5RCH2Cl3.6-3.8RCH2Br3.4-3.6RCH2I3.1-3.3OCH32.1-2.6ArH6.0-9.5H2.5-3.1RCOOH10-13ArOH4.5-7.7Chemical ShiftsChapter Eight Infrared Spectro

18、scopy and Nuclear Magnetic Resonance SpectroscopyInfrared Spectra of Hydrocarbons and Some CommonFunctional GroupsInterpreting(解析解析) Infrared SpectraThe Nature of NMR AbsorptionsNuclear Magnetic Resonance SpectroscopyChemical Shifts1H NMR SpectroscopyIntroduction of Structure Determination Electroma

19、gnetic RadiationInfrared Spectroscopy of Organic Molecules1H NMR Spectroscopy1. Factors affecting the chemical shift (1). The effect of electronegativity (電負(fù)性電負(fù)性)CH3X (CH3 )4Si CH4 CH3I CH3Br CH3CI CH3FX電負(fù)性 1.8 2.1 2.5 2.8 3.1 4.0化學(xué)位移 0 0.23 2.16 2.68 3.05 4.02electronegativity is strongerthe electr

20、on density around the nuclei is lowernuclei are less strongly shieldedchemical shift move to the lower fieldCH3CH2ClCHHHCHHCl0123PPM1H NMR SpectroscopyHH1H NMR SpectroscopyBut in fact:The order of chemical shifts:CHCHCHWhy ?HCCchemical shifts :7.27H4.5-5.5The order of electronegativity:C SP C SP2 C

21、SP3:CHCHCHThe order of chemical shifts:and:(2) Magnetic anisotropy effect (磁各向異性效應(yīng)磁各向異性效應(yīng))1H NMR SpectroscopyB0local magnetic fields paralleled 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，在外加磁場作用下，產(chǎn)生

22、一個各向異性的磁場。構(gòu)成化學(xué)鍵的電子，在外加磁場作用下，產(chǎn)生一個各向異性的磁場。使處于使處于化學(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-即磁各向即磁各向異性。異性。 1H NMR SpectroscopyB0B0= 9.410 ppm = 4.55.7 ppmB0 = 4.55.7 ppm = 6.09.0 ppm1H NMR SpectroscopyCH3CH2ClCHHHCHHClHH0123PPM1H NMR SpectroscopyThe absorption of a proton splits into multiple peaks a

23、 multiplet.three peaks (a triplet) 三重峰三重峰four peaks (a quartet) 四重峰四重峰Called spin-spin splitting(自旋偶合自旋偶合), the phenomenon of multiple absorptions is caused by the interaction, or coupling of the spins of nearby nuclei.多重峰多重峰Coupling is a reciprocal(相互的相互的) interaction between two adjacent groups of

24、 protons.1H NMR SpectroscopyBO1H NMR singnal of HaThe local magnetic fields produced by HbHb 的磁矩將的磁矩將Ha的核磁信號分裂成強(qiáng)度的核磁信號分裂成強(qiáng)度相同的二重峰相同的二重峰BO1H NMR SpectroscopyNumber of equivalent Type of multiplet Ratio of adjacent protons observed intensities 0 Singlet (單峰單峰) 1 1 Doublet (二重峰二重峰) 1:1 2 Triplet (三重峰三重

25、峰) 1:2:1 3 Quartet (四重峰四重峰) 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)偶合常數(shù)), denoted J.nJabcoupling constant (Hz

26、)CHCHab1H 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-單峰單峰，d-雙峰雙峰，t-三重峰三重峰，q-四重峰，四重峰，m-多重峰多重峰3JHH = 7.5 Hz1H NMR SpectroscopyNo splitting occursCCHaHbFaFbSplitting occurs 分子中一組核，化學(xué)位移相同，且對組外任一核的偶合分子中一組核，化學(xué)位移相同，且對組外任一核的偶合常數(shù)也都相同。則這組核稱為常數(shù)也都相

27、同。則這組核稱為磁等同核磁等同核 磁等同核磁等同核之間的偶合作用之間的偶合作用不產(chǎn)生峰的分裂不產(chǎn)生峰的分裂，只有，只有磁不磁不等同核等同核之間的偶合才會之間的偶合才會產(chǎn)生峰的分裂產(chǎn)生峰的分裂。CH2F22. Interpreting (解析解析) 1H NMR spectroscopy1H NMR Spectroscopy1H NMR spectroscopy can give us the following information: 1. 1. 吸收峰的組數(shù)吸收峰的組數(shù)-有幾類不同的有幾類不同的H核；核； 2. 2. 峰的面積（積分強(qiáng)度）峰的面積（積分強(qiáng)度）-每類每類H的相對數(shù)目；的相對數(shù)

28、目； 3. 3. 峰的裂分?jǐn)?shù)目峰的裂分?jǐn)?shù)目-鄰位等性鄰位等性H核的數(shù)目；核的數(shù)目； 4. 4. 峰的位置（峰的位置（值）值）-各類型各類型H所處的化學(xué)環(huán)境；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 SpectroscopyCHR = 1.0 ppm 附附近近CHX = 3.0 - 4.0 ppmCHC=CCH = 2.0 ppm 附附近近1H NMR SpectroscopyCCH = 4.0 - 6.0 ppm

29、CCH = 2.5 ppmArH =7.0 ppm 附附近近1. Predict the pattern of the following compounds:(1)(CH3)2C=C(CH3)2(A)(CH3CH2)2C=CH2(B)(A)(B)(2)ClCH2OCH3ClCH2CH2OH(A)(B)(4)CH3CCl2CH2ClCH3CHClCHCl2one singletone triplet + one quartet + one doubletone singlet + one singlet one triplet + one triplet + one singletone singletone quartet + one doubletone singlet + one singlet one doublet + one doublet+ one multiplet1H NMR Spectroscopy(A)(B) CH3CHBr2(3)BrCH2CH2Br2. Propose structures for compounds w