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Table of characteristic frequencies in infrared spectroscopy

 

This approach is based on experimental observations and comes from a careful comparison of many spectra.

Substance classGroupAbsorption range, cm –1IntensityComments (1)
Alkanes and alkyl fragmentsC – H shaft.3000-2840variableOutside the usual range, C – H stretching vibrations appear for methyl ethers (2850-2815), other ethers (2880-2830), oxirane and aziridine (3050-3000), amines (2820-2780), cyclopropane and cyclohexane (3100 —3050, 3035—2995).
CH def.1470-1430
1395-1365
1250-800
mean
mean
variable
The absorption bands in the 1250-800 region are of no practical importance.
CH def.1475-1450
770-720
average
average
C – D shaft.2200-2080
Alkenes= CH shaft.3095-3075averageOften several stripes.
= CH shaft.3040-3010averageOften several stripes.
= CH def.1420-1290 ( flat ) 1005-675 ( out-of-plane )Out-of-plane oscillations are of no practical importance.
C = C shaft.1690-1635variableFor trans- disubstituted alkenes – 1690-1665 of low intensity, for cis -isomers – 1665-1635. For tri- and tetrasubstituted alkenes, it is in the range of 1690-1650 and is often absent. The frequency decreases when conjugated with another C = C-bond (1650, 1600), triple bond (1600), nitrile group (1620), carbonyl group (1630), benzene ring (1630).
Alkyne≡C – H shaft.3340-3250strongThe same region contains the bands of stretching vibrations O – H and N – H.
C≡C shaft.2260-2100weakFor terminal alkynes, vibrations of the triple bond appear at the low-frequency end of this range. In symmetrical structures, the band is often absent.
≡C – H def.700-600strongAt 1370-1220, a wide and weak overtone of this oscillation is manifested.
Alicyclic compoundsC – H shaft.3090-2860strong
H – C – H def.1470-1430weak
C = C def.1780-1610variable
Aromatic hydrocarbonsC – H shaft.3080-3030A set of stripes is often observed. Stretching vibrations of C – H bonds in alkenes fall into the same region.
C – C1625-1575, 1525-1475averageOften there are two stripes.
combinational2000-1650very weakBy the nature of absorption in this area, the type of substitution of the aromatic ring is established.
C – H def.variable
strong
Out-of-plane absorption bands are used to determine the type of substitution in aromatic compounds.
Organofluorine compoundsC – F shaft.1400-1000strongMore than one band is often observed due to the presence of rotational isomers .
S – F shaft.815-755strong
P – F shaft.1110-760
Si – F shaft.980-820
B – F shaft.1500-800
Organochlorine compoundsC – Cl shaft.1100-1020, 830- <600strong
C – Cl def.400-280average
P – Cl shaft.<600
Si – Cl shaft.<625
B – Cl shaft.1100-650
Organobromine compoundsC – Br shaft.1080-1000, 700-500strong
C – Br def.350-250average
Organoiodine compoundsC – I shaft.650-450strongTwo or more stripes.
C – I def.300-50average
Alcohols and phenolsO – H shaft.3650-3200variableThe absorption bands of hydroxyl groups bound by hydrogen bonds have an increased width and are shifted to a lower frequency region (3550-3450) compared to free (3650-3590).
O – H def. flat1450-1200averageThere is no practical relevance.
C – O shaft.1260-970strongPrimary alcohols: 1075-1000, secondary alcohols: 1125-1000, tertiary alcohols: 1210-1100, phenols: 1275-1150.
O – H def. out-of-plane.<700averageThere is no practical relevance.
Ethers and acetalsC – O – C shaft. asim.1310-1000strongSometimes the band is split into 3, 4 or 5 components.
C – O – C shaft. Sim.1055-870strongSometimes several stripes.
PeroxidesO – O – H shaft.3450-3200variable
C – O – O shaft.1200-1000strong
O – O shaft.1000-800medium or weakThe assignment is unreliable.
AminesNH shaft.3500-3300variablePrimary amines give two narrow bands in this region. When a hydrogen bond is formed, the vibration frequency decreases, and the bands broaden. Sometimes free and hydrogen-bonded forms are observed simultaneously.
NH shaft.3450-3300variableSecondary amines give only one lane. When a hydrogen bond is formed, the vibration frequency decreases, and the bands broaden. Sometimes free and hydrogen-bonded forms are observed simultaneously.
NH + , NH + , NH shaft.3000-2000averageWide, highly structured strip.
NH def.1650-1590, 850-700medium or weak
NH def.1650-1550, 850-700weak
NH + , NH + , NH def.1600-1460averageMore than one band is often observed. The band is weak for aliphatic amines.
C – N shaft.1400-1000averageThere is no practical value.
Nitro compounds and nitroso compoundsNO shaft. asim.1660-1490very strong
NO shaft. Sim.1390-1260strong
N = O shaft.1680-1450 (monomers), 1420-1250 (dimers)very strong
C – N shaft.≈850 (alip. Nitroso compounds), ≈1100 (arom. Nitroso compounds)
Imines and oximesC = N shaft.1690-1520usually strong
O – H shaft.3600-2700strong
O – H def.1475-1315There is no practical value.
Azo compoundsN = N shaft.1500-1400very weakNot present in high-symmetry connections.
Nitriles and isonitrilesC≡N shaft.2260-2240medium or strong
Diazo compounds+ ≡N shaft.2310-2130averageThe frequency depends on the anion.
C = N + = N shaft.2050-2010very strong
Cyanates and isocyanatesOC≡N shaft.2260-2130medium or strong
C – O shaft.1200-1080strong
N = C = O shaft. asim.2280-2230strong
N = C = O shaft. Sim.1450-1380weak
Thiocyanates and thioisocyanatesSC≡N shaft.2170-2130average
C – S shaft.750-550Often two stripes.
N = C = S shaft. asim.2200-2050very strongUsually two bands, Fermi resonance
N = C = S shaft. Sim.950-650
Thiols and sulfidesS – H shaft.2600-2540weak
S – H def.915-800weakThere is no practical value.
C – S shaft.710-570weakThere is no practical value.
S – S shaft.≈500weakThere is no practical value.
Sulfoxides and sulfonesS = O shaft.1225-980strongSometimes several stripes.
SO shaft.1420-1000very strong
S – O shaft.870-690variable
AldehydesC – H comb.2900-2800, 2780-2680weakFermi resonance.
C = O shaft.1765-1645strongAliphatic aldehydes give a band at 1740-1720 cm –1 . In the presence of conjugation, the vibration frequency decreases: aromatic aldehydes (1710-1685), α, β-unsaturated aldehydes (1695-1660). For α-halogenaldehydes, this frequency is higher (1765-1730).
KetonesC = O shaft.1775-1650strongAliphatic ketones give a band at 1715 cm –1 . Conjugation shifts the band towards lower frequencies (aromatic ketones: 1690, α, β-unsaturated ketones: 1675). α-Diketones absorb at 1720 cm –1 , β-diketones – at 1720 and 1650 cm –1 (keto form and enol form, respectively).
Carboxylic acidsCOO – H shaft.3550-2500variableIn strongly dilute solutions, a narrow band appears at 3550–3500 cm –1 . With the formation of hydrogen bonds, the frequency decreases, and the band broadens.
C = O shaft.1800-1650strongFree groups absorb at 1800-1740 cm –1 , in the presence of hydrogen bonds, the frequency decreases to 1740-1650 cm –1 . α, β-Unsaturated carboxylic acids: 1715-1690 cm –1 , aromatic carboxylic acids: 1700-1680 cm –1 .
EstersC = O shaft.1790-1650strongAliphatic esters absorb at 1750-1735 cm –1 , when conjugated, this frequency decreases (α, β-unsaturated esters: 1730-1710, aromatic esters: 1730-1715). α-Halogenated derivatives absorb at 1790-1740 cm –1 .
C – O shaft.1330-1050strongTwo bands: an antisymmetric band with a higher frequency and a symmetric band with a lower frequency.
AmidesN – H shaft.3500-3100averagePrimary amides have two bands.
C = O shaft. (amide I)1740-1630strong
N – H def. and N – C = O shaft. (amide II)1630-1510strongThe band is absent in the lactams.
Carboxylic acid anhydridesC = O shaft.1870-1770, 1800-1720strongSymmetrical and asymmetric bands, respectively.
C – O – C shaft.1300-900strongSeveral stripes.
Halides of carboxylic acidsC = O shaft.1820-1750 shaft.strongTypical for acid chlorides. For acid bromides or acid iodides at a lower frequency.
1900-1870 shaft.strongFluoroanhydrides.
C – Hal shaft.1200-500Fluoroanhydrides – 1200-800, acid chlorides – 750-500, acid bromides – 700-500, acid iodides – 600-500.
Organosilicon compoundsSi – H shaft.2250-2090average
Si – H def.1010-700strongUsually two wide stripes.
Si – O shaft.1100-1000, 900- <600
Si – C shaft.850-650
Si – N shaft.1250-830
Si – F shaft.980-820
Si – Cl shaft.<625
Organophosphorus compoundsP – H shaft.2440-2275weak or medium
PO – H shaft.2700-2650weakVery wide band.
POH comb.2300-2250weakVery wide band.
P – O shaft.1260-855
P = O shaft.1300-960strong
P = N shaft.1500-1170
P – C shaft.800-700differentThere is no practical application.
P – H def.1090-910strong
Organoboron compoundsB – H shaft.2640-2200strong
B – O shaft.1380-1310very strong
B – OH shaft.3300-3200Very wide band.
B – N shaft.1550-1330very strong
B – C shaft.1240-620strongFor very asymmetric molecules, there are two bands.
B – F shaft.1500-800
B – Cl shaft.1100-650

 

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