By SpectralBench Editorial Team2 min read
FTIR Spectrum Table — Infrared Functional Groups Chart
This interactive FTIR spectrum table and infrared spectrum chart covers over 80 characteristic absorption frequencies organized by functional group category. Use it as a comprehensive table for IR spectroscopy — search by group name, category, or wavenumber to instantly filter results. Click any bar in the chart or row in the table to see detailed notes, band shape, and example spectra.
The same data powers SpectralBench's FTIR Peak Identifier — the automated tool that detects peaks in your uploaded spectrum and matches them against this infrared spectrum table to assign functional groups with confidence scores. For a guided walkthrough of how to interpret FTIR spectra region by region, see our FTIR interpretation guide.
How to use this chart
- Find your peak position (wavenumber in cm⁻¹) from your spectrum.
- Type the wavenumber into the search box to highlight matching groups in both the chart and the table, or browse the chart visually.
- Use the band shape (broad, sharp, doublet) and intensity (strong, medium, weak) to narrow your assignment — these characteristics are often as diagnostic as position.
- Look for additional corroborating peaks. Most functional groups produce multiple bands — confirming two or three bands from the same group is far more reliable than relying on a single peak.
| Functional Group | Wavenumber Range (cm⁻¹) | Intensity | Band Shape |
|---|---|---|---|
| O-H stretch (hydrogen bonded) | 3200–3550 | Strong | Broad |
| O-H stretch (carboxylic acid) | 2500–3300 | Strong | Broad |
| N-H stretch (1° amine) | 3250–3500 | Medium | Doublet |
| N-H stretch (amide) | 3180–3350 | Medium | Broad |
| C-H stretch (CH₃, CH₂) | 2845–2970 | Strong | Sharp |
| C-H stretch (aromatic) | 3000–3100 | Medium | Sharp |
| ≡C-H stretch (terminal alkyne) | 3260–3330 | Strong | Sharp |
| C≡N stretch (nitrile) | 2210–2260 | Strong | Sharp |
| C=O stretch (ketone) | 1705–1725 | Strong | Sharp |
| C=O stretch (aldehyde) | 1720–1740 | Strong | Sharp |
| C=O stretch (ester) | 1735–1750 | Strong | Sharp |
| C=O stretch (carboxylic acid) | 1700–1725 | Strong | Sharp |
| C=O stretch (amide I) | 1630–1690 | Strong | Sharp |
| C=C stretch (aromatic) | 1450–1615 | Variable | Sharp |
| C=C stretch (alkene) | 1620–1680 | Variable | Sharp |
| NO₂ stretch (nitro) | 1310–1570 | Strong | Sharp |
| C-O stretch (ester C-O-C) | 1150–1300 | Strong | Sharp |
| C-O stretch (alcohol) | 1040–1175 | Strong | Sharp |
| S=O stretch (sulfone) | 1120–1350 | Strong | Sharp |
| Si-O stretch | 1000–1100 | Strong | Broad |
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FTIR Correlation Chart
Hover over a bar for details. Click to expand in the table below. Bars are color-coded by functional group category; opacity reflects band intensity.
Functional Group Frequencies
Alcohols, Phenols
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
O-H stretch (free) | 3610–3670 | strong | sharp | Sharp absorption of non-hydrogen-bonded O-H. Typically seen in dilute solution… | |
O-H stretch (hydrogen bonded) | 3200–3550 | strong | broad | Broad absorption due to hydrogen-bonded O-H groups. The breadth results from t… |
O-H stretch (free)
3610–3670 cm⁻¹
strongsharp
Sharp absorption of non-hydrogen-bonded O-H. Typically seen in dilute solutions or gas phase.
O-H stretch (hydrogen bonded)
3200–3550 cm⁻¹
strongbroad
Broad absorption due to hydrogen-bonded O-H groups. The breadth results from the distribution of H…
Carboxylic Acids
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
O-H stretch (carboxylic acid) | 2500–3300 | strong | broad | Very broad absorption characteristic of carboxylic acid O-H. Often overlaps wi… | |
C=O stretch (carboxylic acid) | 1700–1725 | strong | sharp | Carbonyl stretch of carboxylic acids. Dimeric hydrogen bonding in the solid an… | |
O-H bend (carboxylic acid) | 1395–1440 | medium | sharp | In-plane bending of the O-H in carboxylic acids, coupled with C-O stretching. … |
O-H stretch (carboxylic acid)
2500–3300 cm⁻¹
strongbroad
Very broad absorption characteristic of carboxylic acid O-H. Often overlaps with C-H stretches, cr…
C=O stretch (carboxylic acid)
1700–1725 cm⁻¹
strongsharp
Carbonyl stretch of carboxylic acids. Dimeric hydrogen bonding in the solid and liquid phase lower…
O-H bend (carboxylic acid)
1395–1440 cm⁻¹
mediumsharp
In-plane bending of the O-H in carboxylic acids, coupled with C-O stretching. This band is less di…
Amines
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
N-H stretch (1° amine, asymmetric) | 3350–3500 | medium | doublet | The higher-frequency component of the primary amine doublet, arising from asym… | |
N-H stretch (1° amine, symmetric) | 3250–3400 | medium | doublet | The lower-frequency component of the primary amine doublet, arising from symme… | |
N-H stretch (2° amine) | 3310–3500 | weak | sharp | A single, weaker N-H stretch band for secondary amines. Because only one N-H b… | |
N-H bend (1° amine, scissors) | 1580–1650 | medium | sharp | Scissoring deformation of the NH₂ group in primary amines. This band helps con… | |
C-N stretch (aliphatic amine) | 1020–1250 | medium | sharp | C-N stretching in aliphatic amines. This band is often difficult to identify w… | |
C-N stretch (aromatic amine) | 1250–1360 | strong | sharp | C-N stretching in aromatic amines (arylamines). The band is stronger and at hi… | |
N-H wag (1° amine) | 650–900 | variable | broad | Broad out-of-plane wagging of the NH₂ group in primary amines. This band is of… | |
N-H wag (2° amine) | 700–750 | weak | broad | Broad, weak out-of-plane wagging of the N-H bond in secondary amines. This ban… |
N-H stretch (1° amine, asymmetric)
3350–3500 cm⁻¹
mediumdoublet
The higher-frequency component of the primary amine doublet, arising from asymmetric N-H stretchin…
N-H stretch (1° amine, symmetric)
3250–3400 cm⁻¹
mediumdoublet
The lower-frequency component of the primary amine doublet, arising from symmetric N-H stretching.…
N-H stretch (2° amine)
3310–3500 cm⁻¹
weaksharp
A single, weaker N-H stretch band for secondary amines. Because only one N-H bond is present, a si…
N-H bend (1° amine, scissors)
1580–1650 cm⁻¹
mediumsharp
Scissoring deformation of the NH₂ group in primary amines. This band helps confirm primary amines …
C-N stretch (aliphatic amine)
1020–1250 cm⁻¹
mediumsharp
C-N stretching in aliphatic amines. This band is often difficult to identify with certainty becaus…
C-N stretch (aromatic amine)
1250–1360 cm⁻¹
strongsharp
C-N stretching in aromatic amines (arylamines). The band is stronger and at higher frequency than …
N-H wag (1° amine)
650–900 cm⁻¹
variablebroad
Broad out-of-plane wagging of the NH₂ group in primary amines. This band is often broad and variab…
N-H wag (2° amine)
700–750 cm⁻¹
weakbroad
Broad, weak out-of-plane wagging of the N-H bond in secondary amines. This band is often obscured …
Amides
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
N-H stretch (amide) | 3180–3350 | medium | broad | Broad N-H stretch in amides, shifted to lower frequency compared to amines due… | |
C=O stretch (amide I) | 1630–1690 | strong | sharp | The amide I band, primarily C=O stretching mixed with some C-N stretching and … | |
N-H bend (amide II) | 1510–1570 | strong | sharp | The amide II band, primarily N-H in-plane bending mixed with C-N stretching. I… |
N-H stretch (amide)
3180–3350 cm⁻¹
mediumbroad
Broad N-H stretch in amides, shifted to lower frequency compared to amines due to resonance with t…
C=O stretch (amide I)
1630–1690 cm⁻¹
strongsharp
The amide I band, primarily C=O stretching mixed with some C-N stretching and N-H bending. The low…
N-H bend (amide II)
1510–1570 cm⁻¹
strongsharp
The amide II band, primarily N-H in-plane bending mixed with C-N stretching. In proteins, this ban…
Alkanes
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C-H stretch (CH₃ asymmetric) | 2950–2970 | strong | sharp | Asymmetric stretching of the three C-H bonds in a methyl group. This band at ~… | |
C-H stretch (CH₃ symmetric) | 2860–2885 | strong | sharp | Symmetric stretching of a methyl group where all three C-H bonds extend and co… | |
C-H stretch (CH₂ asymmetric) | 2915–2940 | strong | sharp | Asymmetric stretching of methylene C-H bonds, appearing near 2925 cm⁻¹. Partic… | |
C-H stretch (CH₂ symmetric) | 2845–2870 | medium | sharp | Symmetric stretching of methylene C-H bonds near 2855 cm⁻¹. Slightly lower in … | |
C-H bend (CH₃ asymmetric deformation) | 1440–1465 | medium | sharp | Asymmetric bending (deformation) of the methyl group near 1450 cm⁻¹. This band… | |
C-H bend (CH₃ symmetric umbrella) | 1370–1390 | medium | sharp | Symmetric bending (umbrella mode) of CH₃ near 1375 cm⁻¹. Gem-dimethyl groups (… | |
C-H bend (CH₂ scissors) | 1440–1475 | medium | sharp | Scissoring deformation of methylene groups near 1465 cm⁻¹. In crystalline long… |
C-H stretch (CH₃ asymmetric)
2950–2970 cm⁻¹
strongsharp
Asymmetric stretching of the three C-H bonds in a methyl group. This band at ~2960 cm⁻¹ is one of …
C-H stretch (CH₃ symmetric)
2860–2885 cm⁻¹
strongsharp
Symmetric stretching of a methyl group where all three C-H bonds extend and contract in phase. Its…
C-H stretch (CH₂ asymmetric)
2915–2940 cm⁻¹
strongsharp
Asymmetric stretching of methylene C-H bonds, appearing near 2925 cm⁻¹. Particularly strong in lon…
C-H stretch (CH₂ symmetric)
2845–2870 cm⁻¹
mediumsharp
Symmetric stretching of methylene C-H bonds near 2855 cm⁻¹. Slightly lower in frequency than the C…
C-H bend (CH₃ asymmetric deformation)
1440–1465 cm⁻¹
mediumsharp
Asymmetric bending (deformation) of the methyl group near 1450 cm⁻¹. This band overlaps with the C…
C-H bend (CH₃ symmetric umbrella)
1370–1390 cm⁻¹
mediumsharp
Symmetric bending (umbrella mode) of CH₃ near 1375 cm⁻¹. Gem-dimethyl groups (isopropyl, t-butyl) …
C-H bend (CH₂ scissors)
1440–1475 cm⁻¹
mediumsharp
Scissoring deformation of methylene groups near 1465 cm⁻¹. In crystalline long-chain alkanes, this…
Alkenes
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
=C-H stretch (alkene) | 3020–3100 | medium | sharp | Stretching of C-H bonds on sp²-hybridized carbon in alkenes. The higher freque… | |
C=C stretch (alkene) | 1620–1680 | variable | sharp | Stretching of the C=C double bond. The band is often weak in symmetrically sub… | |
=C-H oop bend (trans alkene) | 960–975 | strong | sharp | Strong out-of-plane C-H bending for trans-disubstituted alkenes near 970 cm⁻¹.… | |
=C-H oop bend (cis alkene) | 650–730 | medium | sharp | Out-of-plane C-H bending for cis-disubstituted alkenes. This band is weaker an… | |
=C-H oop bend (vinyl/terminal) | 905–920 | strong | sharp | Strong out-of-plane C-H bending for monosubstituted (vinyl) alkenes near 910 c… | |
=C-H oop bend (vinylidene) | 880–900 | strong | sharp | Out-of-plane C-H bending for vinylidene (1,1-disubstituted) alkenes near 890 c… |
=C-H stretch (alkene)
3020–3100 cm⁻¹
mediumsharp
Stretching of C-H bonds on sp²-hybridized carbon in alkenes. The higher frequency compared to sp³ …
C=C stretch (alkene)
1620–1680 cm⁻¹
variablesharp
Stretching of the C=C double bond. The band is often weak in symmetrically substituted alkenes and…
=C-H oop bend (trans alkene)
960–975 cm⁻¹
strongsharp
Strong out-of-plane C-H bending for trans-disubstituted alkenes near 970 cm⁻¹. This band is one of…
=C-H oop bend (cis alkene)
650–730 cm⁻¹
mediumsharp
Out-of-plane C-H bending for cis-disubstituted alkenes. This band is weaker and more variable in p…
=C-H oop bend (vinyl/terminal)
905–920 cm⁻¹
strongsharp
Strong out-of-plane C-H bending for monosubstituted (vinyl) alkenes near 910 cm⁻¹. A second oop ba…
=C-H oop bend (vinylidene)
880–900 cm⁻¹
strongsharp
Out-of-plane C-H bending for vinylidene (1,1-disubstituted) alkenes near 890 cm⁻¹. This single str…
Aromatics
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C-H stretch (aromatic) | 3000–3100 | medium | sharp | Stretching of aromatic C-H bonds on sp² carbons. Appears just above 3000 cm⁻¹,… | |
C=C stretch (aromatic, ~1600 cm⁻¹) | 1585–1615 | variable | sharp | One of the characteristic aromatic ring C=C stretching vibrations near 1600 cm… | |
C=C stretch (aromatic, ~1475 cm⁻¹) | 1450–1510 | variable | sharp | The second major aromatic ring C=C stretching vibration near 1475-1500 cm⁻¹. T… | |
C-H oop bend (monosubstituted aromatic) | 730–770 | strong | sharp | Out-of-plane C-H bending of five adjacent aromatic hydrogens in monosubstitute… | |
Ring oop bend (monosubstituted aromatic) | 690–710 | strong | sharp | Out-of-plane ring bending of monosubstituted benzene near 700 cm⁻¹. This band … | |
C-H oop bend (1,2-disubstituted/ortho) | 735–770 | strong | sharp | Out-of-plane C-H bending of four adjacent aromatic hydrogens in ortho-disubsti… | |
C-H oop bend (1,3-disubstituted/meta) | 770–810 | strong | sharp | Out-of-plane C-H bending of three adjacent hydrogens in meta-disubstituted ben… | |
Ring oop bend (1,3-disubstituted/meta) | 680–720 | strong | sharp | Out-of-plane ring bending for meta-disubstituted benzene. This band near 690 c… | |
C-H oop bend (1,4-disubstituted/para) | 800–860 | strong | sharp | Out-of-plane C-H bending of two adjacent hydrogens in para-disubstituted benze… | |
Ring breathing (aromatic) | 990–1010 | variable | sharp | Symmetric ring expansion/contraction (breathing mode) of aromatic rings near 1… |
C-H stretch (aromatic)
3000–3100 cm⁻¹
mediumsharp
Stretching of aromatic C-H bonds on sp² carbons. Appears just above 3000 cm⁻¹, helping distinguish…
C=C stretch (aromatic, ~1600 cm⁻¹)
1585–1615 cm⁻¹
variablesharp
One of the characteristic aromatic ring C=C stretching vibrations near 1600 cm⁻¹. Intensity depend…
C=C stretch (aromatic, ~1475 cm⁻¹)
1450–1510 cm⁻¹
variablesharp
The second major aromatic ring C=C stretching vibration near 1475-1500 cm⁻¹. Together with the ~16…
C-H oop bend (monosubstituted aromatic)
730–770 cm⁻¹
strongsharp
Out-of-plane C-H bending of five adjacent aromatic hydrogens in monosubstituted benzene. This band…
Ring oop bend (monosubstituted aromatic)
690–710 cm⁻¹
strongsharp
Out-of-plane ring bending of monosubstituted benzene near 700 cm⁻¹. This band paired with the C-H …
C-H oop bend (1,2-disubstituted/ortho)
735–770 cm⁻¹
strongsharp
Out-of-plane C-H bending of four adjacent aromatic hydrogens in ortho-disubstituted benzene. The a…
C-H oop bend (1,3-disubstituted/meta)
770–810 cm⁻¹
strongsharp
Out-of-plane C-H bending of three adjacent hydrogens in meta-disubstituted benzene near 780 cm⁻¹. …
Ring oop bend (1,3-disubstituted/meta)
680–720 cm⁻¹
strongsharp
Out-of-plane ring bending for meta-disubstituted benzene. This band near 690 cm⁻¹ overlaps with th…
C-H oop bend (1,4-disubstituted/para)
800–860 cm⁻¹
strongsharp
Out-of-plane C-H bending of two adjacent hydrogens in para-disubstituted benzene near 830 cm⁻¹. Th…
Ring breathing (aromatic)
990–1010 cm⁻¹
variablesharp
Symmetric ring expansion/contraction (breathing mode) of aromatic rings near 1000 cm⁻¹. This vibra…
Alkynes
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
≡C-H stretch (terminal alkyne) | 3260–3330 | strong | sharp | Stretching of the C-H bond on sp-hybridized carbon in terminal alkynes. The hi… | |
C≡C stretch (terminal alkyne) | 2100–2140 | weak | sharp | Stretching of the carbon-carbon triple bond in terminal alkynes. The band is r… | |
C≡C stretch (internal alkyne) | 2190–2260 | weak | sharp | Stretching of the carbon-carbon triple bond in internal alkynes. Symmetrically… |
≡C-H stretch (terminal alkyne)
3260–3330 cm⁻¹
strongsharp
Stretching of the C-H bond on sp-hybridized carbon in terminal alkynes. The high frequency reflect…
C≡C stretch (terminal alkyne)
2100–2140 cm⁻¹
weaksharp
Stretching of the carbon-carbon triple bond in terminal alkynes. The band is relatively weak becau…
C≡C stretch (internal alkyne)
2190–2260 cm⁻¹
weaksharp
Stretching of the carbon-carbon triple bond in internal alkynes. Symmetrically substituted interna…
Aldehydes
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C-H stretch (aldehyde, Fermi doublet low) | 2700–2760 | medium | doublet | The lower component of the aldehyde C-H Fermi resonance doublet. This distinct… | |
C-H stretch (aldehyde, Fermi doublet high) | 2820–2860 | medium | doublet | The higher component of the aldehyde C-H Fermi resonance doublet, arising from… | |
C=O stretch (aldehyde) | 1720–1740 | strong | sharp | Carbonyl stretch of aldehydes, slightly higher than ketones due to less induct… |
C-H stretch (aldehyde, Fermi doublet low)
2700–2760 cm⁻¹
mediumdoublet
The lower component of the aldehyde C-H Fermi resonance doublet. This distinctive band near 2720 c…
C-H stretch (aldehyde, Fermi doublet high)
2820–2860 cm⁻¹
mediumdoublet
The higher component of the aldehyde C-H Fermi resonance doublet, arising from Fermi resonance bet…
C=O stretch (aldehyde)
1720–1740 cm⁻¹
strongsharp
Carbonyl stretch of aldehydes, slightly higher than ketones due to less inductive donation. Confir…
Nitriles
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C≡N stretch (nitrile) | 2210–2260 | strong | sharp | Strong stretching absorption of the C≡N triple bond. Conjugation lowers the fr… |
C≡N stretch (nitrile)
2210–2260 cm⁻¹
strongsharp
Strong stretching absorption of the C≡N triple bond. Conjugation lowers the frequency, while elect…
Azides
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
N₃ asymmetric stretch (azide) | 2090–2160 | strong | sharp | Strong asymmetric stretching of the azide (-N₃) group. This intense band in an… |
N₃ asymmetric stretch (azide)
2090–2160 cm⁻¹
strongsharp
Strong asymmetric stretching of the azide (-N₃) group. This intense band in an otherwise quiet spe…
Isocyanates
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
N=C=O stretch (isocyanate) | 2250–2275 | strong | sharp | Intense asymmetric stretching of the cumulated N=C=O system. The very strong, … |
N=C=O stretch (isocyanate)
2250–2275 cm⁻¹
strongsharp
Intense asymmetric stretching of the cumulated N=C=O system. The very strong, sharp band in a rela…
Isothiocyanates
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
N=C=S stretch (isothiocyanate) | 2050–2110 | strong | sharp | Intense asymmetric stretching of the cumulated N=C=S system. Appears at lower … |
N=C=S stretch (isothiocyanate)
2050–2110 cm⁻¹
strongsharp
Intense asymmetric stretching of the cumulated N=C=S system. Appears at lower frequency than isocy…
Ketones
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C=O stretch (ketone) | 1705–1725 | strong | sharp | Strong carbonyl stretch of simple aliphatic ketones near 1715 cm⁻¹. The C=O st… | |
C=O stretch (conjugated ketone) | 1665–1700 | strong | sharp | Carbonyl stretch lowered by conjugation with a C=C double bond or aromatic rin… |
C=O stretch (ketone)
1705–1725 cm⁻¹
strongsharp
Strong carbonyl stretch of simple aliphatic ketones near 1715 cm⁻¹. The C=O stretch is typically t…
C=O stretch (conjugated ketone)
1665–1700 cm⁻¹
strongsharp
Carbonyl stretch lowered by conjugation with a C=C double bond or aromatic ring. The extended delo…
Esters
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C=O stretch (ester) | 1735–1750 | strong | sharp | Carbonyl stretch of simple esters, appearing at higher frequency than ketones … | |
C=O stretch (α,β-unsaturated ester) | 1715–1735 | strong | sharp | Carbonyl stretch of esters conjugated with a double bond. Conjugation lowers t… | |
C-O stretch (ester C-O-C) | 1150–1300 | strong | sharp | C-O stretching of the ester linkage. This strong band, combined with the C=O s… |
C=O stretch (ester)
1735–1750 cm⁻¹
strongsharp
Carbonyl stretch of simple esters, appearing at higher frequency than ketones due to mesomeric ele…
C=O stretch (α,β-unsaturated ester)
1715–1735 cm⁻¹
strongsharp
Carbonyl stretch of esters conjugated with a double bond. Conjugation lowers the frequency compare…
C-O stretch (ester C-O-C)
1150–1300 cm⁻¹
strongsharp
C-O stretching of the ester linkage. This strong band, combined with the C=O stretch near 1740 cm⁻…
Anhydrides
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C=O stretch (anhydride, symmetric) | 1800–1850 | strong | sharp | The higher-frequency symmetric C=O stretch of anhydrides. The characteristic t… | |
C=O stretch (anhydride, asymmetric) | 1720–1775 | strong | sharp | The lower-frequency asymmetric C=O stretch of anhydrides. Cyclic anhydrides sh… |
C=O stretch (anhydride, symmetric)
1800–1850 cm⁻¹
strongsharp
The higher-frequency symmetric C=O stretch of anhydrides. The characteristic two-band carbonyl pat…
C=O stretch (anhydride, asymmetric)
1720–1775 cm⁻¹
strongsharp
The lower-frequency asymmetric C=O stretch of anhydrides. Cyclic anhydrides show a stronger high-f…
Acyl Halides
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C=O stretch (acyl halide) | 1770–1815 | strong | sharp | Carbonyl stretch of acyl halides, at high frequency due to the strong electron… |
C=O stretch (acyl halide)
1770–1815 cm⁻¹
strongsharp
Carbonyl stretch of acyl halides, at high frequency due to the strong electron-withdrawing inducti…
Lactones
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C=O stretch (lactone) | 1735–1770 | strong | sharp | Carbonyl stretch of cyclic esters (lactones). Ring strain in smaller lactones … |
C=O stretch (lactone)
1735–1770 cm⁻¹
strongsharp
Carbonyl stretch of cyclic esters (lactones). Ring strain in smaller lactones shifts the frequency…
Carbonates
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C=O stretch (carbonate) | 1720–1780 | strong | sharp | Carbonyl stretch of organic carbonates. The frequency depends on whether the c… |
C=O stretch (carbonate)
1720–1780 cm⁻¹
strongsharp
Carbonyl stretch of organic carbonates. The frequency depends on whether the carbonate is cyclic o…
Ureas
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C=O stretch (urea) | 1640–1690 | strong | sharp | Carbonyl stretch of urea derivatives, lowered significantly by resonance donat… |
C=O stretch (urea)
1640–1690 cm⁻¹
strongsharp
Carbonyl stretch of urea derivatives, lowered significantly by resonance donation from two flankin…
Nitro Compounds
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
NO₂ asymmetric stretch | 1500–1570 | strong | sharp | Strong asymmetric stretching of the nitro group. This band, paired with the sy… | |
NO₂ symmetric stretch | 1310–1370 | strong | sharp | Symmetric stretching of the nitro group near 1340 cm⁻¹. Always look for the co… |
NO₂ asymmetric stretch
1500–1570 cm⁻¹
strongsharp
Strong asymmetric stretching of the nitro group. This band, paired with the symmetric stretch near…
NO₂ symmetric stretch
1310–1370 cm⁻¹
strongsharp
Symmetric stretching of the nitro group near 1340 cm⁻¹. Always look for the corresponding asymmetr…
Imines
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C=N stretch (imine/oxime) | 1620–1690 | variable | sharp | Stretching of the C=N double bond in imines and oximes. The frequency overlaps… |
C=N stretch (imine/oxime)
1620–1690 cm⁻¹
variablesharp
Stretching of the C=N double bond in imines and oximes. The frequency overlaps with C=C stretches …
Alcohols
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C-O stretch (1° alcohol) | 1040–1085 | strong | sharp | C-O stretching vibration of primary alcohols. The position near 1050 cm⁻¹ help… | |
C-O stretch (2° alcohol) | 1085–1125 | strong | sharp | C-O stretching vibration of secondary alcohols near 1100 cm⁻¹. The shift from … | |
C-O stretch (3° alcohol) | 1125–1175 | strong | sharp | C-O stretching vibration of tertiary alcohols near 1150 cm⁻¹. The highest freq… | |
O-H bend (in-plane, alcohol) | 1230–1320 | medium | sharp | In-plane bending (deformation) of the O-H bond in alcohols. This band couples … |
C-O stretch (1° alcohol)
1040–1085 cm⁻¹
strongsharp
C-O stretching vibration of primary alcohols. The position near 1050 cm⁻¹ helps distinguish primar…
C-O stretch (2° alcohol)
1085–1125 cm⁻¹
strongsharp
C-O stretching vibration of secondary alcohols near 1100 cm⁻¹. The shift from the primary alcohol …
C-O stretch (3° alcohol)
1125–1175 cm⁻¹
strongsharp
C-O stretching vibration of tertiary alcohols near 1150 cm⁻¹. The highest frequency among alcohols…
O-H bend (in-plane, alcohol)
1230–1320 cm⁻¹
mediumsharp
In-plane bending (deformation) of the O-H bond in alcohols. This band couples strongly with adjace…
Ethers
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C-O-C stretch (ether) | 1060–1150 | strong | sharp | Asymmetric stretching of the C-O-C linkage in ethers. Aliphatic ethers absorb … |
C-O-C stretch (ether)
1060–1150 cm⁻¹
strongsharp
Asymmetric stretching of the C-O-C linkage in ethers. Aliphatic ethers absorb near 1120 cm⁻¹, whil…
Sulfoxides
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
S=O stretch (sulfoxide) | 1030–1070 | strong | sharp | Strong stretching of the S=O bond in sulfoxides near 1050 cm⁻¹. The single S=O… |
S=O stretch (sulfoxide)
1030–1070 cm⁻¹
strongsharp
Strong stretching of the S=O bond in sulfoxides near 1050 cm⁻¹. The single S=O band distinguishes …
Sulfones
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
S=O stretch (sulfone, asymmetric) | 1290–1350 | strong | sharp | Asymmetric stretching of the two S=O bonds in sulfones. This band, paired with… | |
S=O stretch (sulfone, symmetric) | 1120–1170 | strong | sharp | Symmetric stretching of the two S=O bonds in sulfones near 1150 cm⁻¹. Always c… |
S=O stretch (sulfone, asymmetric)
1290–1350 cm⁻¹
strongsharp
Asymmetric stretching of the two S=O bonds in sulfones. This band, paired with the symmetric stret…
S=O stretch (sulfone, symmetric)
1120–1170 cm⁻¹
strongsharp
Symmetric stretching of the two S=O bonds in sulfones near 1150 cm⁻¹. Always confirm by checking f…
Haloalkanes
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C-F stretch | 1000–1400 | strong | sharp | Stretching of the C-F bond. The high electronegativity of fluorine produces a … | |
C-Cl stretch | 550–800 | strong | sharp | Stretching of the C-Cl bond. Multiple C-Cl bonds (as in CHCl₃) give multiple b… | |
C-Br stretch | 500–680 | strong | sharp | Stretching of the C-Br bond at lower frequency than C-Cl due to the heavier br… |
C-F stretch
1000–1400 cm⁻¹
strongsharp
Stretching of the C-F bond. The high electronegativity of fluorine produces a very strong absorpti…
C-Cl stretch
550–800 cm⁻¹
strongsharp
Stretching of the C-Cl bond. Multiple C-Cl bonds (as in CHCl₃) give multiple bands in this region.…
C-Br stretch
500–680 cm⁻¹
strongsharp
Stretching of the C-Br bond at lower frequency than C-Cl due to the heavier bromine atom. The band…
Phosphorus Compounds
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
P=O stretch | 1150–1300 | strong | sharp | Strong stretching of the P=O bond in phosphates, phosphonates, and phosphine o… |
P=O stretch
1150–1300 cm⁻¹
strongsharp
Strong stretching of the P=O bond in phosphates, phosphonates, and phosphine oxides. The position …
Organosilicon
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
Si-O stretch | 1000–1100 | strong | broad | Strong, broad Si-O stretching absorption. Commonly seen in silicones, silicate… | |
Si-CH₃ deformation | 1240–1280 | strong | sharp | Symmetric deformation of Si-CH₃ groups near 1260 cm⁻¹. This sharp, strong band… |
Si-O stretch
1000–1100 cm⁻¹
strongbroad
Strong, broad Si-O stretching absorption. Commonly seen in silicones, silicates, and glass. In pol…
Si-CH₃ deformation
1240–1280 cm⁻¹
strongsharp
Symmetric deformation of Si-CH₃ groups near 1260 cm⁻¹. This sharp, strong band is highly character…
Epoxides
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C-O stretch (epoxide ring) | 1230–1280 | strong | sharp | Asymmetric C-O-C stretching of the strained three-membered epoxide ring. The r… |
C-O stretch (epoxide ring)
1230–1280 cm⁻¹
strongsharp
Asymmetric C-O-C stretching of the strained three-membered epoxide ring. The ring strain raises th…
Phenols
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C-O stretch (phenol) | 1170–1250 | strong | sharp | C-O stretching of the phenolic C-O bond, with partial double-bond character fr… |
C-O stretch (phenol)
1170–1250 cm⁻¹
strongsharp
C-O stretching of the phenolic C-O bond, with partial double-bond character from conjugation with …
Thioethers
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
C-S stretch | 570–710 | weak | sharp | Stretching of the C-S bond. The band is weak because the small dipole moment c… |
C-S stretch
570–710 cm⁻¹
weaksharp
Stretching of the C-S bond. The band is weak because the small dipole moment change during vibrati…
Boronic Acids
| Functional Group | Range (cm⁻¹) | Intensity | Shape | Notes | |
|---|---|---|---|---|---|
B-O stretch | 1310–1380 | strong | sharp | Strong stretching of the B-O bond in boronic acids and boronate esters. The ba… |
B-O stretch
1310–1380 cm⁻¹
strongsharp
Strong stretching of the B-O bond in boronic acids and boronate esters. The band position is sensi…
Don't want to look up peaks manually? Upload your spectrum to the FTIR Peak Identifier and get automated assignments with confidence scores.
Infrared Spectrum Chart — How to Read FTIR Absorption Bands
An infrared spectrum chart plots wavenumber (cm⁻¹) against transmittance or absorbance, with each dip or peak corresponding to a specific bond vibration. The IR spectrum functional groups listed in the table above are organized by the spectral region where they absorb — from O-H and N-H stretches at high wavenumbers down through the fingerprint region below 1500 cm⁻¹. Understanding this layout makes it easier to use any FTIR data table for systematic peak assignment.
Notes on Using IR Spectroscopy Tables
- Wavenumber ranges are approximate — exact peak positions depend on the molecular environment, substituent effects, and the physical state of the sample.
- Hydrogen bonding shifts O-H and N-H stretches to lower wavenumbers and broadens the bands significantly. A “free” O-H at 3650 cm⁻¹ may shift below 3000 cm⁻¹ in strongly hydrogen-bonded systems like carboxylic acid dimers.
- Conjugation with double bonds or aromatic rings lowers the C=O stretching frequency by 20–40 cm⁻¹. An α,β-unsaturated ketone absorbs near 1680 cm⁻¹ rather than 1715 cm⁻¹.
- Solid-state (KBr pellet, ATR) and solution spectra may show different peak positions and intensities. ATR correction can partially compensate, but always note which technique was used when comparing spectra.
- Never assign a functional group based on a single peak. Cross-reference multiple diagnostic bands — for example, confirm an ester by finding both a C=O stretch near 1740 cm⁻¹ and a strong C-O stretch near 1240 cm⁻¹.
Related Resources
- FTIR Spectrum Interpretation Guide — step-by-step workflow for reading FTIR spectra
- FTIR Peak Identifier — automated peak detection and functional group assignment
- ATR-FTIR Spectroscopy Guide — how ATR works and when to use it
- Spectroscopy Unit Converter — convert between wavenumber, wavelength, frequency, and energy
Frequently Asked Questions
What is an FTIR spectrum table?
An FTIR spectrum table (also called an IR correlation table) is a reference chart listing the characteristic infrared absorption frequencies of common functional groups. Each entry shows the wavenumber range (in cm⁻¹), expected intensity (strong, medium, or weak), band shape (broad, sharp, doublet), and the functional group responsible. Spectroscopists use these tables to identify unknown compounds by matching observed peaks to known absorption ranges.
How do you read an infrared spectrum chart?
Start at the high-wavenumber end (4000 cm⁻¹) and work toward the fingerprint region (below 1500 cm⁻¹). Look for broad O-H or N-H stretches around 3200–3600 cm⁻¹, sharp C-H stretches near 2800–3100 cm⁻¹, strong carbonyl (C=O) bands between 1630–1850 cm⁻¹, and the complex fingerprint region below 1500 cm⁻¹. Match each observed band's position, intensity, and shape against a reference table to assign functional groups.
How do I identify functional groups in an IR spectrum?
Identify functional groups by matching observed absorption bands to known wavenumber ranges: O-H stretches produce broad bands near 3200–3550 cm⁻¹, C=O stretches give strong sharp peaks between 1630–1850 cm⁻¹, and C-H stretches appear as sharp bands near 2800–3100 cm⁻¹. Always consider intensity and band shape alongside position — a broad band at 3300 cm⁻¹ suggests O-H (alcohol), while a medium doublet at the same position suggests N-H (primary amine). Confirm assignments by looking for corroborating peaks from the same functional group.
What wavenumber range indicates an O-H group in FTIR?
Free (non-hydrogen-bonded) O-H stretches appear as a sharp peak near 3610–3670 cm⁻¹. Hydrogen-bonded O-H in alcohols and phenols produces a broad band at 3200–3550 cm⁻¹. Carboxylic acid O-H is even broader, spanning 2500–3300 cm⁻¹ and often overlapping with C-H stretches. The breadth of the O-H band directly reflects the strength and variety of hydrogen bonding in the sample.
What is the difference between FTIR and IR spectroscopy?
IR (infrared) spectroscopy is the general technique of measuring how molecules absorb infrared light. FTIR (Fourier-Transform Infrared) is the modern implementation that uses an interferometer and Fourier transform mathematics to collect the entire spectrum simultaneously, rather than scanning one wavelength at a time. FTIR is faster, more sensitive, and has better wavelength accuracy than older dispersive IR instruments. Today, virtually all IR spectrometers use FTIR technology.