Spectroscopic Identification of Organic Molecules. Infrared Spectroscopy

Transcription

1 2/3 pectroscopic Identification of rganic Molecules Infrared pectroscopy Exclusively for the summer course at East China University of cience and Technology Prepared by Professor angho Koo ot for sale or distribution but only for the class 1

2 Infrared pectroscopy 1. Introduction The range between 4000 cm -1 ~ 400 cm -1 is of practical use. ear I (14,290~4000 cm -1 ); Far I (700~200 cm -1 ) ormally complex spectrum related with vibro-rotational motion of molecule is obtained. Identification of certain functional groups Peak-by-peak correlation identification with authentic sample 2. Theory Infrared radiation in the range 10,000~100 cm -1 is absorbed and converted by organic molecule into energy of molecular vibration. The vibrational spectra appear as bands rather than as lines because a single vibrational energy change is accompanied by a number of rotational energy changes. Band Intensities can be expressed either as transmittance (T) or Absorbance (A). Transmittance (T): the ratio of the radiant power transmitted by a sample to the radiant power incident on the sample: I/I 0 x 100 (%) Absorbance (A): A = log 10 (1/T) 2

3 The frequency of absorption depends on 1 the relative masses of the atoms, 2 the force constants of the bonds, and the geometry of the atoms. Band positions in I are presented as wavenumber (1/cm or cm -1 ) Wavenumber (cm -1 ) = 1/λ (cm) vs. Frequency (z or s -1 ) = c/λ, where or c = 3 x cm/s. ooke s law (harmonic oscillator model of two masses) Force constant Deuteration tudy. M C M /(M C + M ) M C M /(M C ) = M (M C >>M ) Frequency(C )/ frequency(c D) = (2/1) 1/2 olvents for I 3

4 C 2 may react with primary and secondary amines Types of molecular vibration stretching (change of inter-atomic distance) and bending (change of bond angle). Vibrations that result in a rhythmical change in the dipole moment of the molecule are observed in I. Degrees of freedom Each atom has three degrees of freedom corresponding to the Cartesian coordinates (x, y, z) necessary to describe its position relative to other atoms in the molecule. A molecule of n atoms has 3n degrees of freedom. 4

5 Molecular motions: translational, vibrational, and rotational motions For nonlinear molecules, 3 degrees of freedom describe translation and 3 degrees of freedom describe rotation; the remaining 3n 6 degrees of freedom are vibrational degrees of freedom (fundamental vibrations). Linear molecules: 3n 5 vibrational degrees of freedom (2 degrees of freedom are required to describe rotation). 5

6 Interpretation of pectra 1. The high-frequency portion ( cm -1 ) functional group region The characteristic stretching frequencies of,, and C= etc. trong skeletal bands for aromatics and hetero-aromatics in cm The low-frequency portion ( cm -1 ) The lack of strong absorption bands indicates non-aromatic structure. Aromatics display strong out-of-plane C bending and ring bending absorption. Broad, moderately intense absorption suggests the presence of carboxylic acid dimers, amines, or amides (out-of-plane bending) 3. The intermediate portion ( cm -1 ) finger-print region Interacting vibrational modes are observed. pecific structure can be assigned. The C C absorption band in cm -1 makes it possible to assign a specific structure to the alcohol compounds (). 4. Characteristic Group Absorptions of rganic Molecules Qualitative analysis of peak frequencies ν (X ) > ν (C X) > ν (C X) > δ (X ) > ν (C X) > δ (C X) (X = C,, ) Alkanes Four vibrations: ν (C ), δ (C ), ν (C C), δ (C C) ν (C C) is week, and appears in the broad region of cm -1. 6

7 δ (C C) occurs at very low frequencies (below 500 cm -1 ) 1 C tretching Vibrations ν (C ): cm -1. Methyl group: 2962 (as) and 2872 (s) Methylene group: 2926 (as) and 2853 (s) yper-conjugation effect lower ν (C ): cm -1 (as). C sym. ' sym. C asym. ' asym. C C C 3 C C C 2 cf. C (as), 2873 (s) C 2 C (as), 2874 (s) 2 C bending Vibrations Methyl group: 1450 (as) 1375 (s) Methylene group: scissoring (1465), rocking (720); wagging, and twisting ( ) sym. in-phase asym. out-of-phase Geminal dimethyl splitting strong doublet (resonance) at and cm -1. 7

8 More -character in the C bonding gives higher value in ν (C ). Functional group ybridization ν (C ) (% s-character) C sp (50) sp 2 (33) C C sp 2 aromatic (33) 3030 C C 3 sp 3 (25) 2962 (as) 2872 (s) C 2 sp 3 (25) 2926 (as) 2853 (s) sp 3 (25) C 2890 elected examples (1) teric compression ν (C-) (2) Cyclopropanes: angle strain (high s-character in C bond) s (32%) 3050 (as) prismane s (35%) 3066 (as) 2 /Pt cm -1 disappeared (3) alides ν (C ) F Br I C 3 X asym sym C 2 X 2 asym sym CX Br Br

9 Alkenes 1. ν (C ) olefinic: > 3000 cm ν (C ) saturated 3. ν (C=C): cm -1 (m~w) 4. δ (C ) in-plane bending 5. δ (C ) out-of-plane bending: cm -1 ν (C=C): 1650 cm -1 Moderate (m) to weak (w) absorption for unconjugated alkenes. Tetra-substituted C=C can not be detected unless, is not attached. 1 Enol ethers: (strong) Ph Δν = 53 cm -1 cf. C 3 ν (C=) Δν = 53 cm -1 2 Conjugated double bonds C C C ' ν (C=C) lower wave-number, stronger ε δ (C ) trans cm -1 δ (C ) cis , cm -1 Examples 1704 (ν C= ) 1585 (ν C=C ) C 3 C 2 C 2 C (ν C= ) (ν C=C ) 983 (δ C- ) C 3 C 2 C 2 C (ν C= ) (ν C=C ) 975 (δ C- ) 662 trong ν (C=C) in s-cis-conjugation If ν (C=) ν (C=C) > 75 cm -1, ν (C=) and ν (C=C) are 1720 (s) 1640 (s) comparable in intensities. If ν (C=) ν (C=C) < 75 cm -1, ν (C=) is stronger than ν (C=C) as in s-trans-configuration. δ (C ) out-of-plane bending (s) (s) (s) (s) (m) (m) often ambiguous 9

10 Examples Aromatics 1. ν (C ): cm vertone and combination bands: cm ν (C=C): cm -1 (1600, 1580, 1500, 1450 cm -1 ) 4. δ (C ) in-plane bending: cm δ (C ) out-of-plane bending: < 900 cm

11 ubstitution patterns can be distinguished by overtone/combination bands and out-of-plane bending. 11

12 12

13 13

14 14

15 X Y & X=Y=Z Groups ν: cm -1 X, Y, Z = C,, Acetylenes ν (C C): sharp, absent in symmetrical molecule 1 C C ν (C C): cm -1 (w), no band for the symmetrically substituted alkynes ν ( C ): cm -1 (s) δ ( C ): cm -1 (s) Examples C 3 C C : 2150 (m) C 3 C 2 C C : 2120 (m) (C 3 ) 2 C C C : 2135 (m) (C 2 ) 5 C C : 2140 (m) 2 C C ν (C C): cm -1 (w) Examples C 3 C C C 4 9 : 2210 (w) C 2 5 C C C 3 7 : 2190 (vw) C 2 5 C C (C 2 ) 3 : 2260 (vw) C 3 (C 2 ) 3 C C C 2 C C : 2240, 2300, 2135, 3300 (ν C ) 3 Conjugation with a double bond or a phenyl group shift to a lower frequency C C C C : 2033 C 3 (C 2 ) 3 C=C C C: 2114, 1618 (ν C=C ) 4 Conjugation with a C= group ν (C C): not much change, but intensity increases 1675 C 3 C C C C C C C C

16 itriles ( C ) ν C : cm -1, Intensity: sharp and variable The intensity is diminished if an oxygen-containing group is present near C C bond 1/3~1/4 of the normal intensity 1 Aliphatic C : 2250 ± 10 cm -1 Ν CC 2 C 2 C 2 C : Aromatic C : 2235 ± 5 cm -1 C C Conjugation with a C=C double bond: 2225 ± 8 cm -1 C C=C C 2 C 2 C Isonitriles ( + C ) ν C: Aliphatic cm -1, Aromatic 2145 cm -1 Very strong intensity ν (C C ) 1594 cm -1 (this peak is absent in nitrile) C Isocyanopupukeanane Δ 3 + I Diazonium alts ( + ) ν + : cm -1, ubstitution effect Donating group: X = (C 3 ) cm -1 Withdrawing group: X = cm -1 X cm -1 ν(c= + = ) X=Y=Z asymmetric ν: ca cm -1 symmetric ν: ca cm -1 (weak and not practical) 16

17 Azide ( = + = ) asymmetric ν: cm -1 (sometimes split) symmetric ν: cm -1 Allene (C=C=C) ν C=C: cm -1 singlet or doublet (vibrational coupling) 1 Terminal allenes: strong δ C=C= C 2 ca. 850 cm -1 2 C=C=C 2 ν(c=c=c) 1957 (vs) δ(c 2 ) 842 (m) 3 C C=C=C (vs) 858 (vs) ( 3 C) 2 C=C=C (s) 845 (vs) c-x=c=c (s) 843 (s) cf. C 1960 C 1940 (w) 2 Terminal allenes conjugated with C 2, C 2, C 2, C, C ν C=C Doublet 2 C C C C , 1900 (s) 850 (s) nc 4 9 C C C 2 cf. cf. 3 C Ph C C C (s) nc 4 9 C C C 860 (s) 3 C C , 1910 (s) 855 (s) 1960 (s) 3 trained allenes: above 2000 cm -1 C 2020 C 2030, C Isocyanates ( =C= + C ) ν: cm -1 very strong Most aromatic / aliphatic =C=: cm -1 But, C 3 =C=: 2231 cm -1 Ketenes ( C=C=) asymmetric ca cm -1 : strong symmetric ca cm -1 Ph 2 C C 2160, 1130 C C 2130 Ph 17

18 Alcohols and Phenols ν ( ), δ ( ), ν (C ) (1) Free ν ( ): no hydrogen-bonded Measurement should be in C 4, which is dried over P 2 5, and concentration should be lower than 0.01 mole/l. primary cm -1 (3640) secondary cm -1 (3628) tertiary cm -1 (3617) phenolic cm -1 ν ( ) of I II III C C 3 C 2 C 3 C 2 C (C 3 ) 2 C C 3 (C 2 ) 2 C C C C C C C 3 (C 3 ) 3 C C 3 C 2 (C 3 ) 2 C C C I II III C (2) Inter- & Intramolecular -bonding 18

19 (2-1) Intermolecular -bonding (concentration dependent) (a) Dimeric association: ~3500 cm -1 Et and Acetone (in C 4 ): 3510 Et and dioxane (in C 4 ): 3510 (alkyl) and diethyl ether: C 3 C C 3 C (b) Polymeric association: cm -1 i) teric effect 1 Et Et (liquid film) polymeric mostly dimeric monomeric (liquid film) 3647 (C 4 solution) no association (monomeric) ii) tereochemical application Δ ν = ν (free) ν (-bonded) Larger Δ ν indicate stronger -bonding borneol isoborneol free (C 2 ) bonded (nujol) Δ ν = (2-2) Intramolecular -bonding (concentration independent) ν () cm -1 (relatively weak) If the band disappeared upon dilution (< M), this must be due to the intermolecular dimeric association. (a) ingle-bridge complex: cm -1 C X X = C halogen nitro etc. i) (C 2 ) n, Me(C 2 ) n 19

20 ν max (ε) 3619 (24) 3645 (20) 3641 (16) Me 3610 (55) Δ ν = 26 Δ ν = (53) 3565 (27) Δ ν = (34) Me 3554 (44) Δ ν = (11) 3640 (29) Δ ν = (36) 3640 (40) Me Δ ν = (56) no intramolecular -bonding ii) estricted rotation C 3 ν (0.005 M in C 4 ) 3642 (ε 19) 3604 (ε 52), Δ ν = (ε 26), Δ ν = (ε 55), Δ ν = 157 iii) Intramolecular diol (--- distance) Δ ν = L Δ ν = 75 cm -1, L = 1.68 Å (1.64 Å) 250 x 10-8 L 74 iv) (b) Chelation ν () ~2700 cm -1, (broad, ε small) 20

21 (c) --- π cm -1, Δ ν = cm -1 1 C 2 =C (C 2 ) n n = , 3619 Δ ν = 16 cm -1 n = , 3596 Δ ν = 39.1 cm -1 n = , 3625 Δ ν = 13 cm -1 C 2 n 2 Benzyl alcohol ν A x 10-3 (integrated intensity) m (3.70) 3635 (4.41) Δ ν = 18.9 p (3.98) 3636 (5.15) Δ ν = 19.5 m (3.74) 3636 (2.88) Δ ν = 19.4 p (3.56) 3635 (2.58) Δ ν = (4.26) 3636 (2.59) Δ ν = 19.2 m-c (4.04) 3636 (2.40) Δ ν = 19.3 p-c (4.33) 3636 (1.75) Δ ν = Phenetyl alcohols 2 m 3598 (3.62) 3625 (0.60) 3636 (1.82) Δ ν = 37.5 p 3598 (3.14) 3623 (0.53) 3635 (2.23) Δ ν = 37.2 C 3 m 3602 (3.34) 3624 (0.66) 3636 (2.14) Δ ν = 33.5 p 3603 (2.96) 3623 (0.69) 3636 (2.19) Δ ν = (2.62) 3626 (0.68) 3636 (2.36) Δ ν = 29.6 m 3611 (2.25) 3625 (0.71) 3635 (2.78) Δ ν = 24.2 p 3610 (2.23) 3625 (0.88) 3635 (2.61) Δ ν = m 3615 (1.20) 3625 (1.52) 3635 (4.29) Δ ν = 20.0 p 3614 (1.37) 3626 (1.42) 3635 (3.99) Δ ν = 21.0 C 2 C 2 C 2 cf. C 2 C 2 C π bonding only when is electron releasing groups C 2 C 2 C 2 C 2 o --- π interaction 21

22 4 Cyclobutenediol Ph Ph --- π 3603 (C 3 ) Ph Ph --- π 3602 (C 3 ) (C 3 ) 5 Cholesterol 3621 cholesterol epicholesterol 6 Cyclopropyl carbinols (3) ν (C ) in alcohols ν C ν Primary econdary Tertiary Phenolic (a) ν (C ): β C α C α' C C Cα'' α-branching: 15 cm -1 α-unsaturation (including phenyl): 30 ing formation between α,α : 50 α-unsaturation & α -branching: 90 α and α unsaturations: 90 α, α, and α unsaturations: 140 (b) ν C (eq ) > ν C (ax ) ν (ax ) > ν (eq ) 22

23 ν C 3 3 Me 3 Ac 3β (eq) α (ax) eq 3 ax C 3 C 3 Ethers (1) aturated ethers: ν C cm -1 (asymmetric), intense Examples C ote also: ν C (C 3 ) cm -1 C 3 C 3 C 3 C (cis) (trans) C 3 C (2) Unsaturated ethers: ν C cm -1 (asymmetric), intense cm -1 (symmetric), weak Intensity increases in ν C=C Examples C 3 C C , 1212 (gas) npr C C (C 2 ) C 2 5 C C (C 2 ) Ph C 2 C C (C 2 ) 1280~1265 cm -1 (3) Epoxides: ν C cm -1 ; ν C (C 2 ) 3050 cm C C C i) 8 μ band: ca cm -1 (symmetric stretching of the epoxide ring) ii) 11 μ band: cm -1 (asymmetric stretching of the epoxide ring) iii) 12 μ band: cm -1 Both 11 μ and 12 μ bands shift to lower frequency when epoxide is conjugated with alkenes or aromatic rings 23

24 Ph (4) Acetals, Ketals: ν C cm -1 ; 3~5 bands (a) Ketals ; ; (asymmetric ν) (symmetric ν) (b) Acetals An additional 1110 (c) Enol Ketal, Acetal ν(c-) ~ ν(c-) ν(c=c) 1635 ν(c=c) 1630 (d) Ketene Ketal cf. enol ether: ν(c-) ; ν(c=c) Me Me Me ν(c -) ν(c=c) Me Me Me 24

25 Amines, Imines, and Ammonium alts Amine ν ( ), δ ( ) in-plane, out-of-plane ν ( ) (1) Free ν ( ) primary ( 2 ) cm -1 (asymmetric) weak cm -1 (symmetric) weak econdary ( ) cm -1 weak Conformational Isomers (a) Ph C 3 Ph C 3 Ph C 3 C 3 3 C 3 C Ph Ph (I) 3444 (II) 3421 (III) 3395 (b) Ph Ph Two ν ( ) bands are observed due to the conformational isomers. ν ( )ax > ν ( )eq 2 C 3 2 C , 3326 asym sym 3384, (2) ν ( ) for hydrogen-bonded 2 and Intermolecular ν ( ) cm -1 Intramolecular ν ( ) cm -1 25

26 Aniline in ether-type solvent: broad peak at cm -1 Aniline in ketone-type solvent: broad peak at and cm -1 2 forms strong hydrogen-bonding with, but does not form with + Et + Et ν (C ) Aliphatic C : (not practical) Aromatic amine: primary secondary tertiary Imine ( C= ) ν ( ): ν (C=): ca (aliphatic), 1640 (aromatic), 1618 (conjugated). Ammonium alts + 4 : (ν + 4 ), : ca (m), : , (scissoring of + 2 ) 3 + : (ν + ) C= + : (ν + ), (m), 1680 (ν C= + ) Bohlmann Bands Quinolizidines having a trans ring fusion show characteristic absorption bands in the cm -1 region. These absorptions result from a specific interaction between the itrogen lone pair and at least two axial s on carbons adjacent to the itrogen atom. 2856, 2807, 2757 cm -1 26

27 b tbu tbu 12b α- 12b β- Carbonyl Compounds (ν C=: cm -1 ) Factors that influence the band shifts (1) External factors Vapor phase: highest ν C= Liquid phase: dilute solution in non-polar solvents (C 4, C 2 ) higher ν C= cf. C 3 has a reasonable acidity + C C lower frequency olid state: polar matrices give lower ν C= (2) Internal factors A. Electronic and steric nature of the substituents esonance (p bonding) vs. Inductive effects (σ bonding) ' ' X Y X Y X Y X Y ' more inductive strongly inductive more resonance It is more difficult to stretch the + C= bond than the C= bond. 27

28 Examples of inductive effect C 3 C 3 C 3 F Br 1840 (liq) 1806 (liq) 1814 (liq) F F Br Br 1928 (gas) 1827 (gas) 1826 (gas) Examples of resonance effect i C 3 'i Me nbu-e (C 4 ) 1712 (C 4 ) tbu i Ph 3 i Ph Phe 1645 (C 4 ) 1637 (C 4 ) 1645 (C 4 ) 1714 (C 4 ) 1723 (C 4 ) 1704 (C 3 ) otes: 1 Esters of chloroformic acid cm -1 C 3 3 C 1786 (C 4 ) 1806 (C 4 ) 2 Methyl benzoates X C 3 X ν C= Br I F C C (C 3 )

29 3 Enol esters ν C=: ~1760 cm -1 ν C=C: ~ cm -1 (strong) ' ''' '' ' ''' '' ' ''' '' e.g (C 4 ) cm -1 (C 4 ) B. Conjugation shift ' ν C= ~1715 Ar Examples 35 cm -1 ' ν C= ~1680 ( ) ν C=: smaller shift ( ) ν(c=c) intensity increases compared with that of isolated C=C. Et 1692 (C 4 ) 1684 (C 4 ) 1704 (C 4 ) 1712 (C 3 ) 1724 (C 3 ) C. teric hindrance: affecting conjugation C 3 ν C= 1680 ν C= 1700 D. ing strains 1 Ketones ν(c=) = θ more s-character in C= ν(c=) θ

30 Examples 2 C C + 2 C 2 C o C 90% 3045 ν(c-) 1813 ν(c=) , 1380 more p-character (liquid) 1746 (C 4 ) more s character in C= 2 Lactones 1841 (C 4 ) 1818 (C 4 ) 1770 (liq) 1774 (C 3 ) 1783 (C 4 ) 1730 (liq) 1732 (C 3 ) 1748 (C 4 ) (C 4 ) Lactams 1840 (C 3 ) 1837 (C 4 ) (liq) 1691 (liq) 1748 (C 2 2 ) 1690 (C 3 ) 1702 (C 4 ) 1651 (KBr) 1667 (C 3 ) 1673 (C 4 ) 1660 (C 3 ) 1671 (C 4 ) Penicillin series C Et 2 C C 2 ' 1708 C 1675 C 1755 E. aloketones dipole-dipole repulsion shifts its ν(c=) to a higher frequency 30

31 Br 1750 A conformation in which dipole-dipole repulsion is minimized Br Br 1764 In general, shift caused by an a-halogen is the following order: I (0~10) < Br (0~20) < (0~25) < F Geometrical factors: o shift when the angle between C= and C X exceeds 90 o. Y Y = Y = Br Y = Y X X = Y = X = Y = Br X = Y = (3) ydrogen bonding A. Carboxylic acid Vapor phase: 1780 cm -1 (monomer); 1730 cm -1 (dimer) intermolecular -bonding Liquid: 1710 cm -1 (dimer) olution: on-polar solvent: 1760 cm -1 (monomer); 1710 cm -1 (dimer) Polar solvent: in ether in alcohol ~920 cm -1 (- out-of-plane bending) B. Intramolecular -bonding involving carbonyl groups Me Me δ Ac 1731 Ac 1734 Ac 1744 Ac

32 ν(c=) 1709 br. band Et 1685 Et Et Et 1712 Et 1733 C 3 Cyclic Keto-esters ν(c=) Ester ν(c=) Ketone Chelated Ester C 2 Et C 2 Et C 2 Et C 2 Et C 2 Et (4) Vibrational couplings Interaction of two vibrating absorptions, which must be close enough to each other, to give splitting into two bands. A. Diones 1721 two peaks for s-cis 1760, (C 4) (C 4) B. Acid anhydrides 1820, 1760 cm -1 : Δν ~ 60 cm -1 (35~90 cm -1 ) Cyclic and linear anhydrides can be distinguished by the intensity comparison of the coupled vibrations. 32

33 1817 (s) 1750 (w) C (w) 1761 (s) C 4 Aldehydes and Ketones A. Aldehydes: characteristic ν(c ) bands at 2820 and 2720 cm -1. B. s-cis enones: increased intensity of ν(c=c) C. Conjugation effects: 1 ν(c=) ν(c=c) (in C 4) mp -28 o C (recrystallized from dry ether at -78 o C) no peak at 1600 cm -1 cf. ν(c=c)

34 4 ν(c=) ν(c=c) (liquid) (C 4 ) (gas) (KBr) D. ing-size dependence E. Trans-annular effects 1 δ δ two bands can be seen by careful analysis 4 4 C X C 3 X , 1684 Carboxylic acids A. ν(c=): 1760 cm -1 monomer, 1710 cm -1 dimer B. δ() out-of-plane ~920 cm -1 (broad) dimeric carboxylic acid C. Conjugation 1 C=C C 2 : 1718 cm -1 (monomer in dioxane) Ar C=C C 2 : 1720 cm -1 (monomer in dioxane) Dimeric conjugated C 2 : cm -1 34

35 X 2 D. Carboxylates X ν(c=) in Me (monomer) ν(c=) in C 4 (dimer) C Et 3 C 3 Et cm -1 (asymmetric) & 1400 cm -1 (symmetric) Esters and Lactones (1) Esters: ν(c=) cm -1 ν(c C) cm -1 two bands (asymmetric and symmetric) Asymmetric band ν(c C) is usually stronger than ν(c=), broad and occasionally split into two C C 3 3 ν(c-) ~1190 cm A. Inductive effect gives higher ν(c=) Me C Me Me ν(c=) 1778 cm B. Vinyl ester, enol ester: higher ν(c=) (2) Lactones A. ing-size dependence B. Conjugation effect 1 ν(c=): 20~30 cm -1 lower than the saturated lactones 1,2- vs. 1,3-diols 1817, 1763 (w) 1777, 1753 (w) 1729 (C 3 ) 1743 (C 4 ) (C=) 1635 (C=C)

36 higher in frequency tronger inductive effect gives higher ν(c=): cm αβ,γδ-unsaturated γ-lactones: ν(c=) is close to that of saturated γ-lactones Pyrones C= C=C C= C=C (KBr) 36

37 C. Polar effect (Inductive effect and dipole-dipole interactions) 1 alogens Br cf. F F F F F F 1873 Br Br cf cf xygens 2 C cf D. teric effects C 2 Me 1743 Acid halides ν(c=): cm -1 for chlorides tronger inductive effect by X induces the increase of ν(c=). X plitting into doublet (Fermi resonance) is frequently observed. mall changes in ν(c=) between gas and condensed phase, and even smaller changes among various solvents. 37

38 F 1840 (liq) 1806 (liq) 1799 (C 4 ) Br 1814 (liq) 1818 (C 4 ) F F 1928 (gas) F 3 C F 1905 (liq) 1901 (gas) F 3 C 1810 (gas) 1 Conjugated Acid alides: cm -1 for chlorides 1762 (C 4 ) 2 Aroyl alides F 1812 (C 4 ) (C 4) (C 2) Br (C 2) I (C 2) Acid anhydrides Asymmetric: 1820 cm -1 ymmetric: 1750 cm -1 Δν ~ (s-as) 1767 (w-s) (C 4) 1802 (w) 1761 (s) (C 4) (C ) 1784 (C 4) (C 4 ) 1779 igher frequency band is more intense for acyclic anhydride, whereas the lower frequency band is stronger for cyclic anhydride. Diacylperoxides Aliphatic: (as), (s), Δν ~25 cm -1 Aromatic: (as), (s), Δν ~25 cm -1 Mixed aliphatic and aromatic: Two bands (C 4) 2 Ph Ph (C 4) (C 4) (nujol) Ph (C 4) 38

39 Amides A Amide I band: ν (C=) 1690(free) 1650( bonded). Amide II band: δ ( 2 deformation) and ν(c ) Amide III band: ν (C ) ν( ) asymmetric free amide: , symmetric free amide: , bonded amide: ote 1 Amide I band: Gas phase ; Dilute solution 1700; Liquid (KBr) 1675 (C 3 ), 1690 (dioxane), 1670 (Me) C (C 4 ) 2 alogen shift (Inductive effect) C (C 3 ) 3 Amide II band: traight chain alkane amides: (dilute solution in C 3, monomer) ew band at 1608 cm -1 appears on higher concentration (in solid, dimer and trimer etc.) B ' Amide I band: ν (C=) 1680 (free), 1655 ( bonded). Amide II band: mainly δ ( ) 1530(free), 1550(associated) Amide III band: δ ( ) 1260 (free), 1300 (associated). ν( ) 3440 (free amide), 3300 (associated), 3070 (unknown origin). ote 1 Amide I band: 1640 (solid phase), 1680 (in dioxane) Electron-withdrawing group on nitrogen gives a band of higher frequency (solid), 1705 (C 3 ) C 3 Anilide: ~1700 cm-1 39

40 Very little effect by conjugation with benzene ring C 3 both at 1649 cm -1 (KBr) C 3 Me (-bonding) cf cm -1 (KBr) C cm -1 (KBr) 2 Amide II band: band at (weak) disappears upon changing to D (solid), 1533 (C3), (dioxane) 3 ν ( ): In cyclic lactams, 3440 (free), 3175 (dimer), and 3070 (associated) C '' ' Amide I band: 1650 cm -1 olvent effect: 1645 (liq) 1628 (C 3 ) 1650 (C 4 ) (liq) 1732 (KBr) 1739 (C 4 ) 1515 Pyridones α-pyridones ν(c=) 1650 cm -1 close to saturated amide (C 3 ) (C 3 ) 1656 (C 3 ) 1653 (nujol) γ-pyridones 1638 (C 3 ) (C 3 ) (C 3 ) 40

41 itro group ν ( ) (s) asymmetric ν ( ) (s) symmetric Conjugation gives lower frequency , cm -1 effected by a substituent on the phenyl group itroso group ν (=): cm -1 C A. econdary itroso Compounds ' ' unstable oxime C (vapor) These bands disappear quickly 1588 cf. oximes 1642 (gas) 1669 (nujol) 1670 (solid) 1662 (nujol) 1667 (C 4 ) 1656 (C 3 ) (C 3 ) B. Tertiary itroso Compound ' '' 1548 (C 4 ) 1513 (C 4 ) The majority of nitroso compounds associate in solution to give a mixture of the cis and trans dimers cf. Ph Ph Ph Ph 1511 (KBr) 1455 (KBr) 41

42 cis dimer (KBr) 1323 trans dimer (KBr) dimer (KBr) cf (KBr) C. itrosamines (lower then any other ν =) 1429 (C 3 ) 1470 (C 4 ) D. itrites ( =) ν (=) (s) asymmetric; (s) symmetric Two bands due to s-trans and s-cis conformations trans (higher) cis (lower) 1650 trans (C 4 ) 1608 cis (C 4 ) E. itrates (liq) (liq) ulfur compounds A. Thiones ν(c=) 1188 Ar Ar' 1220 ν(c=) ν(c=) = 1.6 ~ (liq) 1801 (C 3 ) C 2 : 1522, 650 cm -1. ' ~1200 ~ (C 3 ) Z-isomer P(Et) 3 heat Bz 91% 90% 42

43 B. Thiols (C ) and ulfides ( ) ν ( ) cm -1 (weak) ν (C ) m -1 (medium or weak) C 3 ' cm cm cm -1 ' '' cm -1 Ar cm C. ulfoxides ν (=) cm -1 (very strong) more important I 1072 (C 4 ) 1055 (C 3 ) 1057 (liq) 1020 (C 3 ) 1012 (C 3 ) 1012 (C 3 ) 1232 (KBr) 1231 (nujol) Ar Ar Ar 1045 (C 3 ) 1041 (C 3 ) 1070 (liq) D. ulfones ν (=) cm -1 (very strong) asymmetric ν (=) cm -1 (very strong) symmetric ' 43