第2章 IR part 2

1、2.7 2.7 有机化合物分子中常见基团红外特征吸收有机化合物分子中常见基团红外特征吸收Dipole moment: The greater the change in dipole moment, the moreintense the absorption IR intensitySymmetryElectronegativityVibration : as s 烷烃烷烃 (Alkane)C-H伸缩振动 (Stretch)3000 cm-1 (3000-2840 cm-l) (sp3 C-H) CH3 2960, 2870 cm-1; CH2 2926, 2850 cm-1 CH2变形振动

2、 (Bending) 1465 cm-1 CH3变形振动 (Bending) 1375 cm-1. CH2变形振动(Bending) 720 cm-1 (长链烷烃长链烷烃含4个或以上 CH2). C-CStretch (伸缩振动, 1250-720 cm-l) not interpretatively useful; many weak peaks. CH3 BendC-H StretchCH2 Bend烯烃 (Alkene)=C-HStretch : 3100-3010 cm-1 (sp2 C-H) . =C-HBending: 1000-650 cm-1. C=CStretch: 1660

3、-1600 cm-1. Conjugation moves C=C stretch to lower frequencies and increases the intensity. Symmetrically substituted bonds (e.g., 2,3-dimethyl-2-butene) do not absorb in the infrared (no dipole change). Symmetrically disubstituted (trans) double bonds are often vanishingly weak in absorption; cis a

4、re stronger. 单取代 RCH=CH2 (990,910 cm-1, out-of-plane (oop, 面外) )=C-H Stretch=C-H BendC=C Stretch反式 R1CH=CHR2 (970 cm-1, Out-of-plane (oop, 面外) )C=C Stretch=C-H Bend顺式 R1CH=CHR2 (730-665 cm-1, Out-of-plane (oop, 面外) )=C-H Bend1,1二取代 R1R2CH=CH2 (890 cm-1, Out-of-plane (oop, 面外) )=C-H Bend三取代 R1R2CH=CH

5、R3 (810 cm-1, Out-of-plane (oop, 面外) )=C-H Bend炔烃 (Alkyne)C-HStretch: 3300 cm-1. C CStretch: 2150 cm-1. Conjugation moves stretch to lower frequency. Disubstituted or symetrically substituted triple bonds give either no absorption or weak absorption. C-HBend for sp-hybridized C-H occurs at values be

6、tween 650-600 cm-1. C-H BendC-H StretchC C Stretch 芳香烃 (Aromatic Compounds)C-HStretch: 31003000 cm-1 for sp2 C-H.C-HOut-of-plane (oop) bending: 900-690 cm-1. These bands can be used with great utility to assign the ring substitution pattern. C=CRing stretch: in pairs at 1600 cm-1 and 1475 cm-1. Over

7、tone (倍频)/combination (组合频) bands : 2000 and 1667 cm-1. These weak absorptions can be used to assign the ring substitution pattern. 770-730, 710-690 cm-1770-730 cm-1810-750, 725-680 cm-1860-800 cm-1醇 (Alcohol)O-HFree O-H stretch: 3650-3600 cm-1 (sharp peak ). Hydrogen-bonded O-H: 3400-3300 cm-1 (bro

8、ad peak)C-OStretch: 1260-1000 cm-1. This band can be used to assign a primary, secondary, or tertiary structure to an alcohol. 醚 (Ether)C-OStretch: 1300-1000 cm-1 (prominent band). 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

9、 give two strong bands at about 1250 and 1040 cm-1, while aliphatic ethers give one strong band at about 1120 cm-1. 胺 (Amine)N-HStretch occurs in the range 3500-3300 cm-1. Primary amines: two bands. Secondary amines : one band (a vanishingly weak one for aliphatic compounds and a stronger one for ar

10、omatic secondary amines). Tertiary amines: N-H stretch. N-HBending: 1640-1560 cm-1 (primary), 1500 cm-1 (Secondary amines ). N-HOut-of-plane bending: 800 cm-1. C-NStretch: 1350-1000 cm-1. C-N stretchN-H bendN-H stretchN-H stretchN-H bendC-N stretchC-N stretch醛 (Aldehyde)C=OStretch: 1725 cm-1. Conjug

11、ation moves the absorption to a lower frequency. C-H(-CHO)Stretch: 2750 cm-1 and 2850 cm-1. Note that the C-H stretch in alkyl chains does not usually extend to frequencies as low as 2750 cm-1. 醛基质子的伸缩振动与变形振动的倍频偶合 (Fermi 共振)酮 (Ketone)C=OStretch: 1715 cm-1. Conjugation moves the absorption to a lower

12、 frequency. Ring strain moves the absorption to a higher frequency in a cyclic ketone. C-C (C-CO-C)Bending: 1300-1100 cm-1 (medium-intensity). 羧酸 (Carboxylic Acid)O-HStretch: 3400-2400 cm-1 (very broad, strongly H-bondedand often overlaps the C-H absorptions). C=OStretch: 1730-1700 cm-1 (broad). Con

13、jugation moves the absorption to a lower frequency. C-OStretch: 1320-1210 cm-1 (medium intensity). 酯 (Ester)C=OStretch: 1750-1735 cm-1. Conjugation in the acyl portion of the molecule moves the absorption to a lower frequency; conjugation with the O in the alkoxy portion moves the absorption to a hi

14、gher frequency. Ring strain in cyclic esters (lactones) moves the absorption to a higher frequency. C-OStretch in two or more bands, one stronger and broader than the other, occurs in the range 1300-1000 cm-1. C-O Stretch酰氯 (Acid Chloride)C=OStretch: 1810-1775 cm-1. Conjugation lowers the frequency

15、to 1780-1760 cm-1. C-ClStretch: 730-550 cm-1. C-Cl Stretch酸酐 (Acid Anhydride)C=OStretch: 1830-1800 cm-1 and 1775-1740 cm-1. Conjugation moves the absorption to a lower frequency. Ring strain (cyclic anhydrides) moves the absorptions to a higher frequency. C-O(C-O-C)Stretch: 1300-900 cm-1 (multiple b

16、ands). 酰胺 (Amide)C=OStretch: 1680-1630 cm-1. N-HStretch Primary amides (-NH2) : two bands 3350 and 3180 cm-1 ().Secondary amides (-NH) : one band at 3300 cm-1. N-HBending: 1640-1550 cm-1 for primary and secondary amides. 硝基化合物 (Nitro)N-OAliphatic nitro compounds: asymmetric stretch (strong), 1600-15

17、30 cm-1; symmetric stretch (medium), 1390-1300 cm-1. N-OAromatic nitro compounds (conjugated): asymmetric stretch (strong), 1550-1490 cm-1; symmetric stretch (strong), 1355-1315 cm-1. N-O stretchN-O stretch卤代烷 (Alkyl Halide)C-FStretch (strong): 1400-1000 cm-1. Monofluoroalkanes absorb at the lower-frequency end of this range, while polyfluoroalkanes give multiple strong bands in the range 1350-1100 cm-1. Aryl fluorides absorb between 1250 and 1100 cm-1. C-ClStretch (strong) in aliphatic chlorides: 785-540 cm-1Aryl chlorides absorb between 1100 and 1035