1 Faeshakar

Ir Band Assignment

The following table lists infrared spectroscopy absorptions by frequency regions.

4000-3000 cm-1
3700-3584mediumsharpO-Hstretchingalcoholfree
3550-3200strongbroadO-Hstretchingalcoholintermolecular bonded
3500
3400
medium N-Hstretchingprimary amine 
3400-3300
3330-3250
medium N-Hstretchingaliphatic primary amine 
3350-3310medium N-Hstretchingsecondary amine 
3300-2500strongbroadO-Hstretchingcarboxylic acidusually centered on 3000 cm-1
3200-2700weakbroadO-Hstretchingalcoholintramolecular bonded
3000-2800strongbroadN-Hstretchingamine salt 
       
3000-2500 cm-1
3333-3267strongsharpC-Hstretchingalkyne 
3100-3000medium C-Hstretchingalkene 
3000-2840medium C-Hstretchingalkane 
2830-2695medium C-Hstretchingaldehydedoublet
2600-2550weak S-Hstretchingthiol 
       
2400-2000 cm-1
2349strong O=C=Ostretchingcarbon dioxide 
2275-2250strongbroadN=C=Ostretchingisocyanate 
2260-2222weak CΞNstretchingnitrile 
2260-2190weak CΞCstretchingalkynedisubstituted
2175-2140strong S-CΞNstretchingthiocyanate 
2160-2120strong N=N=Nstretchingazide 
2150  C=C=Ostretchingketene 
2145-2120strong N=C=Nstretchingcarbodiimide 
2140-2100weak CΞCstretchingalkynemonosubstituted
2140-1990strong N=C=Sstretchingisothiocyanate 
2000-1900medium C=C=Cstretchingallene 
2000  C=C=Nstretchingketenimine 
       
2000-1650 cm-1
2000-1650weak C-Hbendingaromatic compoundovertone
       
1870-1540 cm-1
1818
1750
strong C=Ostretchinganhydride 
1815-1785strong C=Ostretchingacid halide 
1800-1770strong C=Ostretchingconjugated acid halide 
1775
1720
strong C=Ostretchingconjugated anhydride 
1770-1780strong C=Ostretchingvinyl / phenyl ester 
1760strong C=Ostretchingcarboxylic acidmonomer
1750-1735strong C=Ostretchingesters6-membered lactone
1750-1735strong C=Ostretchingδ-lactoneγ: 1770
1745strong C=Ostretchingcyclopentanone 
1740-1720strong C=Ostretchingaldehyde 
1730-1715strong C=Ostretchingα,β-unsaturated esteror formates
1725-1705strong C=Ostretchingaliphatic ketoneor cyclohexanone or cyclopentenone
1720-1706strong C=Ostretchingcarboxylic aciddimer
1710-1680strong C=Ostretchingconjugated aciddimer
1710-1685strong C=Ostretchingconjugated aldehyde 
1690strong C=Ostretchingprimary amidefree (associated: 1650)
1690-1640medium C=Nstretchingimine / oxime 
1685-1666strong C=Ostretchingconjugated ketone 
1680strong C=Ostretchingsecondary amidefree (associated: 1640)
1680strong C=Ostretchingtertiary amidefree (associated: 1630)
1650strong C=Ostretchingδ-lactamγ: 1750-1700 β: 1760-1730
       
1670-1600 cm-1
1678-1668weak C=Cstretchingalkenedisubstituted (trans)
1675-1665weak C=Cstretchingalkenetrisubstituted
1675-1665weak C=Cstretchingalkenetetrasubstituted
1662-1626medium C=Cstretchingalkenedisubstituted (cis)
1658-1648medium C=Cstretchingalkenevinylidene
1650-1600medium C=Cstretchingconjugated alkene 
1650-1580medium N-Hbendingamine 
1650-1566medium C=Cstretchingcyclic alkene 
1648-1638strong C=Cstretchingalkenemonosubstituted
1620-1610strong C=Cstretchingα,β-unsaturated ketone 
       
1600-1300 cm-1
1550-1500
1372-1290
strong N-Ostretchingnitro compound 
1465medium C-Hbendingalkanemethylene group
1450
1375
medium C-Hbendingalkanemethyl group
1390-1380medium C-Hbendingaldehyde 
1385-1380
1370-1365
medium C-Hbendingalkanegem dimethyl
       
1400-1000 cm-1
1440-1395medium O-Hbendingcarboxylic acid 
1420-1330medium O-Hbendingalcohol 
1415-1380
1200-1185
strong S=Ostretchingsulfate 
1410-1380
1204-1177
strong S=Ostretchingsulfonyl chloride 
1400-1000strong C-Fstretchingfluoro compound 
1390-1310medium O-Hbendingphenol 
1372-1335
1195-1168
strong S=Ostretchingsulfonate 
1370-1335
1170-1155
strong S=Ostretchingsulfonamide 
1350-1342
1165-1150
strong S=Ostretchingsulfonic acidanhydrous
hydrate: 1230-1120
1350-1300
1160-1120
strong S=Ostretchingsulfone 
1342-1266strong C-Nstretchingaromatic amine 
1310-1250strong C-Ostretchingaromatic ester 
1275-1200
1075-1020
strong C-Ostretchingalkyl aryl ether 
1250-1020medium C-Nstretchingamine 
1225-1200
1075-1020
strong C-Ostretchingvinyl ether 
1210-1163strong C-Ostretchingester 
1205-1124strong C-Ostretchingtertiary alcohol 
1150-1085strong C-Ostretchingaliphatic ether 
1124-1087strong C-Ostretchingsecondary alcohol 
1085-1050strong C-Ostretchingprimary alcohol 
1070-1030strong S=Ostretchingsulfoxide 
1050-1040strongbroadCO-O-COstretchinganhydride 
       
1000-650 cm-1
995-985
915-905
strong C=Cbendingalkenemonosubstituted
980-960strong C=Cbendingalkenedisubstituted (trans)
895-885strong C=Cbendingalkenevinylidene
850-550strong C-Clstretchinghalo compound 
840-790medium C=Cbendingalkenetrisubstituted
730-665strong C=Cbendingalkenedisubstituted (cis)
690-515strong C-Brstretchinghalo compound 
600-500strong C-Istretchinghalo compound 
       
900-700 cm-1
880 ± 20
810 ± 20
strong C-Hbending1,2,4-trisubstituted 
880 ± 20
780 ± 20
(700 ± 20)
strong C-Hbending1,3-disubstituted 
810 ± 20strong C-Hbending1,4-disubstituted or
1,2,3,4-tetrasubstituted
 
780 ± 20
(700 ± 20)
strong C-Hbending1,2,3-trisubstituted 
755 ± 20strong C-Hbending1,2-disubstituted 
750 ± 20
700 ± 20
strong C-Hbendingmonosubstituted
benzene derivative
 

Functional GroupNotesAlkane C-H bonds are fairly ubiquitous and therefore usually less useful in determining structure.

Absorption peaks above 3000 cm-1 are frequently diagnostic of unsaturation





See "Free vs. Hyrdogen-Bonded Hydroxyl Groups" in the Introduction to IR Spectra for more informationPrimary amines produce two N-H stretch absorptions, secondary amides only one, and tetriary none.







The carbonyl stretching absorption is one of the strongest IR absorptions, and is very useful in structure determination as one can determine both the number of carbonyl groups (assuming peaks do not overlap) but also an estimation of which types.As with amines, an amide produces zero to two N-H absorptions depending on its type.

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