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1、江南大学超值-划算-购物推荐群： 302284607,Charpter 3 Infrared Spectroscopy,Vibrational portion,Fig. 3.1 the Relationship of the infrared region to others included in the electromagnetic Spectrum,红外光,Table 3.1 IR Range,Fig. 3.2 The Infrared Spectrum of polystyrene,3.1 The Infrared Absorption Process,Molecules are e
2、xcited to a higher energy state when they absorb IR radiation. 8-40 kJ/mole, selectively Radiation in this energy range corresponds to the range encompassing the stretching and bending vibrational frequencies of the bonds in most covalent molecules. Increase the amplitude of the vibrational motion.
3、Only those bonds which have a dipole moment that changes as a function of time are capable of absorbing IR radiation. Symmetric bonds, such as those of H2 or Cl2, do not absorb infrared radiation.,Symmetric or pseudosymmetric,A bond must present an electrical dipole which is changing at the same fre
4、quency as the incoming radiation in order for energy to be transferred. The changing electrical dipole of the bond can then couple with the sinusoidally changing electromagnetic field of the incoming radiation. A symmetric bond which has identical or nearly identical groups on each end will not abso
5、rb in the infrared.,3.2 Uses of the Infrared Spectrum,The infrared spectrum can be used for molecules much as a fingerprint can be used for humans. The infrared spectrum is to determine structural information about a molecule.,Fig. 3.3 The approximate regions where various common types of bonds abso
6、rb,the Modes of Stretching and Bending,Symmetric Stretch Asymmetric Stretch,Complicated Spectrum?,Fundamental absorptions: the ground state to the lowest-energy state.,Overtones: 2 , 3 , ,Combination bands:,Difference bands:,Fermi resonance: a fundamental vibration couples with an overtone or combin
7、ation band. Carbonyl compounds,Rotational coupling may lead to a considerable amount of unresolved fine structure.,3.4 Bond Properties and Absorption Trends,c- the speed of light K- the force constant - reduced mass,Hooks law:,Stronger bonds have a larger force constant K and vibrate at higher frequ
8、encies than weaker bonds. C-C C=C CC 1200cm-1 1650cm-1 2150cm-1 increasing K,Bending motions occur at lower energy (lower v) than the typical stretching motions because of the lower value for K. CH stretching CH bending 3000cm-1 1340cm-1,Hybridization affects the force constant K， spsp2sp3 sp sp2 sp
9、3 CH = CH CH 3300cm-1 3100cm-1 2900cm-1,Resonance has the effect of reducing the force constant K, and the absorption moves to a lower frequency. C=O (normal) C=O (conjugated) 1715cm-1 1675 1680cm-1,3.5 the Infrared Spectrometer,FT-IR (Fourier Transform Infrared Spectrometer) Greater speed Greater s
10、ensitivity Better signal-to noise,Fig. 3.4 A schematic diagram of a FT-IR Spectrometer,Michelson Interferometer,3.6 Preparation of Samples for Infrared Spectroscopy,Liquids. Salt plate KBr, 4000-400cm-1; NaCl, 4000-650cm-1 Solids. KBr pellet Nujol mull (mineral oil) Solution CCl4 The region around 7
11、85cm-1 is often obscured by the strong C-Cl stretch that occurs there.,Fig. 3.5,Solids: KBr pellet,The main disadvantage of this method is that KBr absorb water. Nujol mull method: grind the compound with mineral oil (Nujol) to create a suspension of the finely ground sample dispersed in the mineral
12、 oil. Nujol bands appear at 2924, 1462, and 1377 cm-1.,Fig. 3.6,Gas,Fig. 3.7 the Gas Cell,3.7 What to Look for When Examining Infrared Spectra,Fig. 3.8 The infrared spectrum of 3-methyl-2-butanone (neat liguid, KBr plates).,Characteristic the position (wavenumbers) the intensity the shape,C=O at 171
13、5cm-1 strong absorption broad peak,1,2,Fig. 3.9 A Comparison of the Intensities of the C=O and C=C Absorption Bands,C=O 1850-1630cm-1 C=C 1680-1620cm-1,Fig. 3.10 A Comparison of the Shapes of the Absorption Bands for the O-H and N-H Groups,O-H 3650-3200cm-1 N-H 3500-3300cm-1,3.8 Correlation Charts a
14、nd Tables,Table 3.2 A Simplified Correlation Chart,Fig. 3.11 Absorption bands of bonds,Table 3.3 Base Values for Absorptions of Bonds,3.9 How to Approach the Analysis of a Spectrum (or what you can tell at a glance),The C=O, O-H, N-H, C-O, C=C, CC, CN, and NO2 peaks are the most conspicuous and give
15、 immediate structural information if they are present. Do not try to make a detailed analysis of the C-H absorptions near 3000cm-1; almost all compounds have these absorptions.,The important gross features,1. Is a carbonyl group present? 1820-1660cm-1, often the strongest absorption and of medium wi
16、dth. If C=O is present: Broad absorption near 3400-2400cm-1O-Hacids Medium absorption near 3400cm-1(or a double peak) N-Hamides Strong-intensity absorptions near 1300-1000cm-1C-Oesters Two C=O absorptions near 1810 and 1760 cm-1anhydrides Two weak absorptions near 2850 and 2750 cm-1aldehydes The pre
17、ceding five choices have been eliminated ketones If C=O is absent: Broad absorption near 3400-3300cm-1O-H, confirm this by finding C-O near 1300-1000cm-1alcohols, phenols Medium absorption(s) near 3400cm-1N-Hamines Check for C-O near 1300-1000cm-1(and absence of O-H near 3400cm-1 ethers,2. Double bo
18、nds and/or aromatic rings,C=C is a weak absorption near 1650cm-1. Medium to strong absorptions in the region 1600-1450cm-1; these often imply an aromatic ring. Confirm the double bond or aromatic ring by consulting the C-H region; aromatic and vinyl C-H occurs to the left of 3000cm-1 (aliphatic C-H
19、occurs to the right of this value). 3. Triple bonds CN is a medium, sharp absorption near 2250cm-1. CC is a weak, sharp absorption near 2150cm-1. Check also for acetylenic C-H near 3300cm-1. 4. Nitro groups Two strong absorptions at 1600-1530cm-1 and 1390-1300cm-1. 5. Hydrocarbons None of the preced
20、ing are found. Major absorptions are in C-H region near 3000cm-1. Very simple spectrum; the only other absorptions appear near 1460 and 1375cm-1.,A. Alkanes,C-H stretch,around 3000cm-1,sp3 C-H 3000 cm-1 (vinylic, aromatic, acetylenic, or cyclopropyl),3.10 Hydrocarbons: Alkane, alkenes, and Alkynes,C
21、-H bending,CH2 1465cm-1(m) CH3 1450cm-1, 1375cm-1(m) A long-chain band (CH2)n bending (rocking), n 4, 720cm-1,C-C stretch not interpretatively useful; many weak peaks,Fig. 3.12 the Infrared Spectrum of Decane （癸烷）,Fig. 3.13 the Infrared Spectrum of mineral oil,Fig. 3.14 the Infrared Spectrum of Cycl
22、ohexane,B. Alkenes,=C-H stretch (sp2) 3000cm-1(m) (3095-3010cm-1) out-of-plane (oop) bending 1000-650cm-1(s),C=C stretch 1660-1600cm-1(m-w),conjugation,moves C=C stretch to the lower frequencies increases the intensity,substituted,symmetrically substituted bonds no absorption symmetrically disubstit
23、uted double bonds trans vanishingly weak cis stronger,Fig. 3.15 the Infrared Spectrum of 1-Hexene,Fig. 3.16 the Infrared Spectrum of Cyclohexene,Fig. 3.17 the Infrared Spectrum of cis-2-Pentene,Fig. 3.18 the Infrared Spectrum of trans-2-Pentene,C-H (sp) stretch near 3300cm-1(s) CC stretch near 2150c
24、m-1(m-w),C. Alkynes,conjugation moves to lower frequency. disubstituted or symmetrically substituted no absorption or weak absorption,Fig. 3.20 the Infrared Spectrum of 4-octyne,Fig. 3.19 the Infrared Spectrum of 1-octyne,Fig. 2.21 the C-H Stretch Region,C-H Stretch Region 3300-2750cm-1,Table 3.4 St
25、retching Vibrations for Various sp3-Hybridized C-H Bonds,Fig. 3.22 the C-H Bending Vibrations for Methyl and Methylene Groups,C-H Bending Vibrations for Methyl and Methylene,Fig. 3.23 C-H Bending Patterns for the Isopropyl and t-butyl Groups,C=C Stretching Vibrations,Simple Alkyl-Substituted Alkenes
26、 1670-1640 cm-1 The C=C frequencies increase as alkyl groups are added to a double bond. mono- 1640cm-1, di- 1650cm-1, tri- and tetra- 1670cm-1 trans-Disubstituted alkenes absorb at higher frequencies(1670cm-1) than cis-disubstituted alkenes (1658cm-1). Rather weak intensity, in many cases (tetrasub
27、stituted), not observed cis-Alkenes (less symmetry) absorb more strongly than trans-alkenes Double bonds in rings absorb more weakly than those not contained in rings. Terminal double bonds in monosubstituted alkenes generally have stronger absorption.,Conjugation Effects,Conjugation moves the peak
28、to the right. vinyl double in styrene 1630cm-1 Conjugated with the C=O, the C=C absorption shifts to lower frequency, and is intensified by the strong dipole of the C=O.,1650 cm-1 1646 1611 1566 1656,Ring-Size Effects with Internal Double Bonds,Fig. 3.24 C=C stretching vibrations in endocyclic syste
29、ms, 1611cm-1,no couple,C-C single-bond stretching vibration can be resolved into two components (a and b). Component a is in line with the C=C stretching vector, the C-C and C=C bonds are coupled, leading to a higher frequency of absorption.,Fig. 3.25 The effect of alkyl substitution on the frequenc
30、y of a C=C bond in a ring,1940 cm-1 1780 1678 1657 1655 1651,Ring-Size Effects with External Double Bonds,Fig. 3.26 C=C stretching vibrations in exocyclic systems.,C-H Bending Vibrations for Alkenes,in-plane (scissoring) for terminal alkenes 1415cm-1 (m-w) out-of-plane 1000-650cm-1 (s),Fig. 3.27 The
31、 CH Out-of-plane Bending Vibrations for Substituted Alkenes,C=C 1670cm-1 Very weak,Overtone 1820, vinyl,Monosubstituted double bonds Two strong bands for alkyl-substituted, 990, 910 Release electrons groups (Cl, F, OR) shift the 910 band to right, 810 Withdraw electrons groups (C=O, CC) shift the ba
32、nd to left, 960 1,2-Disubstituted double bonds cis- , 700, and trans-, 970 1,1-disubstituted double bonds, 890 Trisubstituted double bonds, 815 Tetra-, no absorption,=C-H stretch(sp2) 3000cm-1 =C-H oop 900-690cm-1 C=C ring stretch 1600cm-1, 1475cm-1 Overtone/combination bands 2000-1667cm-1,3.11 Arom
33、atic rings,Fig. 3.28 the Infrated Spectrum of Toluene,back,Fig. 3.29 the Infrared Spectrum of ortho-Diethylbenzene,Fig. 3.30 the Infrared Spectrum of meta-Diethylbenzene,Fig. 3.31 the Infrared Spectrum of para-Diethylbenzene,Fig. 3.32 the Infrared Spectrum of Styrene,back,In-plane, 1300-1000cm-1, ra
34、rely useful. Out-of-plane, 900-690cm-1, far more useful, extremely intense, resulting from strong coupling with adjacent H, can be use to assign the position of substituents on the aromatic ring. oop bending vibrations is most reliable for alkyl-, alkoxy-, halo-, amino-, or carbonyl-substituted arom
35、atic compounds. Aromatic nitro compounds, derivatives of aromatic carboxylic acids, and derivatives of sulfonic acids often lead to unsatisfactory interpretation.,C-H Bending Vibrations,Discussion,Reliable interpretation,Unreliable interpretation,Fig. 3.33 C-H out-of-plane Bending Vibrations for Sub
36、stituted Benzenoid Compounds,Substituted Rings,690cm-1, strong; if absent, no mono-；Be obscured by the halocarbon solvents (strong C-X) 750cm-1, strong,750,690 780 880,800-850,720-667cm-1 from C=C oop ring bending,Combinations and Overtone Bands,Weak, these bands are best observed by using neat liqu
37、ids or concentrated solutions. If the compound has a high-frequency carbonyl group, this absorption will overlap the weak overtone bands so that no useful information can be obtained from the analysis of the region. Consistent with the oop bending vibrations,Fig. 3.34 the 2000-to-1667 Region for Sub
38、stituted Benzenoid Compounds,back,3.12 Alcohols and Phenols,O-H stretch free 3650-3600cm-1, sharp peak H-bonded 3400-3300cm-1, broad peak C-O-H bend 1440-1220cm-1, a broad and weak peak C-O stretch 1260-1000cm-1 O-H in-plane bending absorption near 1360cm-1, usually overlaps the C-H bending vibratio
39、n (CH3, 1375cm-1).,Fig. 3.35 The Infrared Spectrum of 1-Hexanol,Fig. 3.36 The Infrared Spectrum of 2-Butanol,Fig. 3.37 The Infrared Spectrum of para-Cresol,O-H Stretching Vibrations,Fig. 3.38 the O-H Stretch Region,dilute solution,Discussion,very dilute solution,pure (neat) liquid film, intermolecul
40、ar H-bonding,Intramolecular H-bonding,Methyl salicylate 3200cm-1 Normal phenols 3350cm-1,Present in ortho-carbonyl-substituted phenols, usually shifts the broad O-H band to right. The intramolecular H-bonded band does not change its position significantly even at high dilution.,C-O-H Bending Vibrati
41、ons coupled to H-C-H bending 1440-1220cm-1, some weak and broad peaks, often obscured by CH3 bendings.,C-O Stretching Vibrations,Strong absorption bands 1260-1000cm-1 The C-O absorptions are coupled with the adjacent C-C stretching vibrations, the position of the band may be used to assign a primary
42、, secondary, or tertiary structure to an alcohol or to determine whether a phenolic compound is present.,O conjugates with the ring shifts the C-O band to left (more double-bond character) 1220cm-1,phenols,Table 3.5 C-O and O-H Stretching Vibrations in Alcohols and Phenols,These C-O absorptions are
43、shifted to lower frequencies when unsaturation is present on adjacent C or when the O-H is attached to a ring. Shifts of 30-40 cm-1 from the base values are common.,Fig. 3.39 the Infrared Spectrum of Propargyl,3.13 Ethers,C-O stretch the most prominent band 1300-1000cm-1 Absence of C=O and O-H is re
44、quired to ensure that C-O stretch is not due to an ester or an alcohol. Phenyl alkyl ethers give to strong bands at about 1250 and 1040 cm-1. Aliphatic ethers give one strong band at about 1120 cm-1.,Fig. 3.40 The Infrared Spectrum of Dibutyl Ether,Fig. 3.41 The Infrared Spectrum of Anisole（茴香醚）,C-O
45、-C stretch 1300-1000cm-1, Vinyl ethers,Alcohols and esters also give strong band,Discussion,1120cm-1 strong asymmetric C-O-C stretching 850cm-1 very weak symmetric stretching band a six-membered ring containing oxygen, 1120cm-1, Dialkyl ethers, Aryl ethers,two strong bands 1250cm-1 1040cm-1,1220cm-1
46、 strong asymmetric C-O-C stretch 850cm-1 very weak symmetric stretch,Through resonance, the C-O band shifted to left because of the increased double-bond character, which strengthens the bond. Resonance increases the polar character of the C=C double bond, the band at 1640 cm-1 is considerably stron
47、ger than in normal C=C absorption.,Resonance 1220cm-1,No resonance 1120cm-1, Epoxides,Small ring compounds usually give three bands: 1280-1230cm-1, weak ring-stretching band 950-815cm-1, strong ring-deformation bands asymmetric 880-750cm-1, strong symmetric mono-, 835cm-1; di-, 775cm-1, Acetals and
48、Ketals,1200-1020cm-1, four or five strong bands these band are often unresolved,3.14 Carbonyl Compounds,aldehydes, ketones, acids, esters, amides, acid chlorides, and anhydrides 1850-1650cm-1, strong absorption C=O stretching frequency is sensitive to attached atoms C=O frequency of a ketone, is usu
49、ally considered the reference point,Fig. 3.42 normal base values for the C=O stretching vibrations for carbony groups,Electron-withdrawing effects (inductive effects) Resonance effects Hydrogen bonding,In acid chlorides, the highly electronegative halogen atom strengthens the C=O bond through an enhan