红外光谱IR

nullnull江南大学超值-划算--购物推荐群： 302284607Charpter 3 Infrared SpectroscopyCharpter 3 Infrared SpectroscopyVibrational portionFig. 3.1 the Relationship of the infrared region to others included in the electromagnetic Spectrum 红外光红外光Table 3.1 IR RangeTable 3.1 IR RangenullFig. 3.2 The Infrared Spectrum of polystyrene3.1 The Infrared Absorption Process3.1 The Infrared Absorption ProcessMolecules are excited 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. 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 pseudosymmetricSymmetric or pseudosymmetricA bond must present an electrical dipole which is changing at the same frequency 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 absorb in the infrared. 3.2 Uses of the Infrared Spectrum3.2 Uses of the Infrared SpectrumThe 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 absorb nullthe Modes of Stretching and Bending Symmetric Stretch Asymmetric Stretch Symmetric Stretch Asymmetric StretchComplicated Spectrum? Complicated Spectrum? Fundamental absorptions: the ground state to the lowest-energy state. Fermi resonance: a fundamental vibration couples with an overtone or combination band. Carbonyl compounds Rotational coupling may lead to a considerable amount of unresolved fine structure. 3.4 Bond Properties and Absorption Trends3.4 Bond Properties and Absorption Trendsc- the speed of light K- the force constant μ- reduced mass Hook’s law:nullStronger bonds have a larger force constant K and vibrate at higher frequencies than weaker bonds. C-C C=C C≡C 1200cm-1 1650cm-1 2150cm-1 increasing KnullBending motions occur at lower energy (lower v) than the typical stretching motions because of the lower value for K. C－H stretching C－H bending ~3000cm-1 ~1340cm-1 Hybridization affects the force constant K， sp>sp2>sp3 sp sp2 sp3 ≡C－H = C－H －C－H 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-13.5 the Infrared Spectrometer3.5 the Infrared SpectrometerFT-IR (Fourier Transform Infrared Spectrometer) Greater speed Greater sensitivity Better signal-to noiseFig. 3.4 A schematic diagram of a FT-IR SpectrometerMichelson Interferometer3.6 Preparation of Samples for Infrared Spectroscopy3.6 Preparation of Samples for Infrared SpectroscopyLiquids. Salt plate KBr, 4000-400cm-1; NaCl, 4000-650cm-1 Solids. KBr pellet Nujol mull (mineral oil) Solution CCl4 The region around 785cm-1 is often obscured by the strong C-Cl stretch that occurs there.Fig. 3.5 Solids: KBr pellet 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 oil. Nujol bands appear at 2924, 1462, and 1377 cm-1. Fig. 3.6 Gas Gas Fig. 3.7 the Gas Cell 3.7 What to Look for When Examining Infrared Spectra3.7 What to Look for When Examining Infrared SpectraFig. 3.8 The infrared spectrum of 3-methyl-2-butanone (neat liguid, KBr plates). Characteristic the position (wavenumbers) the intensity the shapeC=O at 1715cm-1 strong absorption broad peak12nullFig. 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-1nullFig. 3.10 A Comparison of the Shapes of the Absorption Bands for the O-H and N-H GroupsO-H 3650-3200cm-1 N-H 3500-3300cm-13.8 Correlation Charts and Tables3.8 Correlation Charts and TablesTable 3.2 A Simplified Correlation ChartnullFig. 3.11 Absorption bands of bondsTable 3.3 Base Values for Absorptions of BondsTable 3.3 Base Values for Absorptions of Bonds3.9 How to Approach the Analysis of a Spectrum (or what you can tell at a glance)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, C≡C, C≡N, and NO2 peaks are the most conspicuous and give 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 featuresThe important gross features1. Is a carbonyl group present? 1820-1660cm-1, often the strongest absorption and of medium width. If C=O is present: Broad absorption near 3400-2400cm-1→O-H→acids Medium absorption near 3400cm-1(or a double peak) →N-H→amides Strong-intensity absorptions near 1300-1000cm-1→C-O→esters Two C=O absorptions near 1810 and 1760 cm-1→anhydrides Two weak absorptions near 2850 and 2750 cm-1→aldehydes The preceding five choices have been eliminated → ketones If C=O is absent: Broad absorption near 3400-3300cm-1→O-H, confirm this by finding C-O near 1300-1000cm-1→alcohols, phenols Medium absorption(s) near 3400cm-1→N-H→amines Check for C-O near 1300-1000cm-1(and absence of O-H near 3400cm-1 →ethers2. Double bonds and/or aromatic rings2. Double bonds and/or aromatic ringsC=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 occurs to the right of this value). 3. Triple bonds C≡N is a medium, sharp absorption near 2250cm-1. C≡C 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 preceding 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. AlkanesA. AlkanesC-H stretcharound 3000cm-1sp3 C-H < 3000 cm-1 (3000-2840 cm-1) (except strained ring compounds) sp2 and sp C-H > 3000 cm-1 (vinylic, aromatic, acetylenic, or cyclopropyl) 3.10 Hydrocarbons: Alkane, alkenes, and AlkynesC-H bendingC-H bendingCH2 1465cm-1(m) CH3 1450cm-1, 1375cm-1(m) A long-chain band (CH2)n bending (rocking), n ≥4, 720cm-1C-C stretch not interpretatively useful; many weak peaks Fig. 3.12 the Infrared Spectrum of Decane （癸烷） nullFig. 3.13 the Infrared Spectrum of mineral oil Fig. 3.14 the Infrared Spectrum of CyclohexaneB. AlkenesB. 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) conjugationmoves C=C stretch to the lower frequencies increases the intensity substitutedsymmetrically substituted bonds no absorption symmetrically disubstituted double bonds trans vanishingly weak cis strongernullFig. 3.15 the Infrared Spectrum of 1-HexeneFig. 3.16 the Infrared Spectrum of CyclohexenenullFig. 3.17 the Infrared Spectrum of cis-2-PenteneFig. 3.18 the Infrared Spectrum of trans-2-PenteneC. Alkynes≡C-H (sp) stretch near 3300cm-1(s) C≡C stretch near 2150cm-1(m-w)C. Alkynes conjugation moves to lower frequency. disubstituted or symmetrically substituted no absorption or weak absorptionnullFig. 3.20 the Infrared Spectrum of 4-octyneFig. 3.19 the Infrared Spectrum of 1-octynenullFig. 2.21 the C-H Stretch RegionC-H Stretch Region 3300-2750cm-1nullTable 3.4 Stretching Vibrations for Various sp3-Hybridized C-H BondsC-H Bending Vibrations for Methyl and MethyleneFig. 3.22 the C-H Bending Vibrations for Methyl and Methylene GroupsC-H Bending Vibrations for Methyl and MethylenenullFig. 3.23 C-H Bending Patterns for the Isopropyl and t-butyl GroupsC=C Stretching VibrationsC=C Stretching VibrationsSimple Alkyl-Substituted Alkenes 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 (tetrasubstituted), 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 EffectsConjugation moves the peak 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. Ring-Size Effects with Internal Double Bonds Ring-Size Effects with Internal Double Bonds Fig. 3.24 C=C stretching vibrations in endocyclic systems 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.nullFig. 3.25 The effect of alkyl substitution on the frequency of a C=C bond in a ring Ring-Size Effects with External Double Bonds Ring-Size Effects with External Double Bonds Fig. 3.26 C=C stretching vibrations in exocyclic systems.C-H Bending Vibrations for AlkenesC-H Bending Vibrations for Alkenesin-plane (scissoring) for terminal alkenes 1415cm-1 (m-w) out-of-plane 1000-650cm-1 (s)nullFig. 3.27 The C－H Out-of-plane Bending Vibrations for Substituted AlkenesC=C 1670cm-1 Very weakOvertone 1820, vinylMonosubstituted 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, C≡C) shift the band 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 absorption3.11 Aromatic rings=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-13.11 Aromatic ringsFig. 3.28 the Infrated Spectrum of ToluenebacknullFig. 3.29 the Infrared Spectrum of ortho-DiethylbenzeneFig. 3.30 the Infrared Spectrum of meta-DiethylbenzenenullFig. 3.31 the Infrared Spectrum of para-DiethylbenzeneFig. 3.32 the Infrared Spectrum of StyrenebacknullIn-plane, 1300-1000cm-1, rarely 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 aromatic compounds. Aromatic nitro compounds, derivatives of aromatic carboxylic acids, and derivatives of sulfonic acids often lead to unsatisfactory interpretation. C-H Bending VibrationsDiscussion nullReliable interpretationUnreliable interpretationnullFig. 3.33 C-H out-of-plane Bending Vibrations for Substituted Benzenoid CompoundsSubstituted Rings 690cm-1, strong; if absent, no mono-；Be obscured by the halocarbon solvents (strong C-X) 750cm-1, strong750690 780 880800-850 720-667cm-1 from C=C oop ring bending Combinations and Overtone BandsCombinations and Overtone BandsWeak, these bands are best observed by using neat liquids 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 vibrationsFig. 3.34 the 2000-to-1667 Region for Substituted Benzenoid Compoundsback3.12 Alcohols and Phenols3.12 Alcohols and PhenolsO-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 vibration (CH3, 1375cm-1).Fig. 3.35 The Infrared Spectrum of 1-HexanolnullFig. 3.36 The Infrared Spectrum of 2-ButanolFig. 3.37 The Infrared Spectrum of para-CresolnullO-H Stretching VibrationsFig. 3.38 the O-H Stretch Regiondilute solutionDiscussion very dilute solutionpure (neat) liquid film, intermolecular H-bondingIntramolecular H-bondingIntramolecular H-bondingMethyl 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 Vibrations coupled to H-C-H bending 1440-1220cm-1, some weak and broad peaks, often obscured by CH3 bendings. C-O Stretching VibrationsC-O Stretching VibrationsStrong 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, 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-1phenolsnullTable 3.5 C-O and O-H Stretching Vibrations in Alcohols and PhenolsThese C-O absorptions are 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. nullFig. 3.39 the Infrared Spectrum of Propargyl 3.13 Ethers3.13 Ethers C-O stretch the most prominent band 1300-1000cm-1 Absence of C=O and O-H is required 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 EthernullFig. 3.41 The Infrared Spectrum of Anisole（茴香醚）Discussion C-O-C stretch 1300-1000cm-1Alcohols and esters also give strong bandDiscussion 1120cm-1 strong asymmetric C-O-C stretching 850cm-1 very weak symmetric stretching band a six-membered ring containing oxygen, 1120cm-1 two strong bands 1250cm-1 1040cm-1 1220cm-1 strong asymmetric C-O-C stretch 850cm-1 very weak symmetric stretchnullThrough 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 stronger than in normal C=C absorption.null 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 1200-1020cm-1, four or five strong bands these band are often unresolved3.14 Carbonyl Compounds3.14 Carbonyl Compoundsaldehydes, 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 usually considered the reference pointFig. 3.42 normal base values for the C=O stretching vibrations for carbony groupsnullElectron-withdrawing effects (inductive effects) Resonance effects Hydrogen bonding In acid chlorides, the highly electronegative halogen atom strengthens the C=O bond through an enhanced inductive effect and shifts the frequency to even higher values than are found in esters. Explanation Ester Amide Anhydrides Anhydrides Carboxylic acid Shift to higher frequencies because of a concentration of electronegative O Two bandsin monomeric form in very dilute solution, 1760cm-1 in concentrated solution, in the form of neat liquid, or in the solid state (KBr pellet and Nujol) tend to dimerize via H-bonding, weakens the C=O, lowers the force constant K, resulting in a lowering of C=O frequency of saturated acids, 1710cm-1nullKetones absorb at a lower frequency than aldehydes because of their additional alkyl group, which is electron-donating (compared to H) and supplies electrons to the C=O bond. This electron-releasing effect weakens the C=O bond in the ketone and lowers the force constant and the absorption frequency.A. Factors which influence the C=O stretching vibrationA. Factors which influence the C=O stretching vibrationDelocalization of the  electrons in the C=C and C=O bonds. Conjugation increases the single-bond character of the C=O and C=C bonds in the resonance hybrid and hence lowers K, shifts the bands to right. ,  double bond results in 25-45cm-1 lowering of the C=O frequency. Addition of unsaturation ( ,  ) results in a further shift to lower frequency, but only by about 15cm-1 more. The C=C shifts from 1650 to 1640cm-1, and the absorption is greatly intensified.Conjugation EffectsRotational IsomersRotational IsomersOften two closely spaced C=O absorption peaks are observed for these conjugated systems, resulting from two possible conformations, the s-cis and s-trans. The s-cis conformation absorbs at a higher frequency than the s-trans conformation. In some cases, the C=O absorption is broadened rather than split into the doublet. nullConjugation does not reduce the C=O frequency in amides. The introduction of sp2 hybridized C removes electron density from the C=O and strengthens the bond instead of interacting by resonance as in other carbonyl examples. Since the parent amide group is already highly stabilized, the introduction of the C=C does not overcome this resonance. Aryl-substituted aldehye 1725→1700 Ring Size EffectsRing Size EffectsSix-membered rings with C=O are unstrained, 1715cm-1 Decreasing the ring size increases the frequency of the C=O All of the functional groups listed in Fig. 3.45, which can form rings, give increased frequencies of absorption with increased angle strain. For ketones and esters, there is often a 30cm-1 increase in frequency for each C removed from the unstrained six-membered ring values. In ketones, larger rings have frequencies which range from nearly the same value as in cyclohexanone to values slightly less than 1715 cm-1. eg. Cycloheptanone, 1705cm-1. -Substitution EffectsWhen the C next to the C=O is substituted with a chlorine (or other halogen) atom, the C=O band shifts to a higher frequency. The electron-withdrawing effect removes electrons from the C of the C=O bond. This removal is compensated for by a tightening of the  bond (shortening), which increases the force constant and leads to an increase in the absorption frequency.  -Substitution EffectsEquatorial chlorine ~1750cm-1 When the Cl is next to C=O, nonbonded electrons on the O are repelled, resulting in a stronger bond and a higher absorption frequency. Axial chlorine ~1725cm-1Hydrogen-Bonding EffetsHydrogen-Bonding Effets H bonding to C=O lengthens the C=O bond and lowers the stretching force constant K, resulting in a lowering of the absorption frequency.1680cm-11710cm-1Ketone Tautomer of ,  -Diketone ~1720cm-1 (doublet)Enol Tautomer of