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IR Spectroscopy Chart (Correlation Table)
A searchable infrared absorption table for organic functional groups. Type a peak position to see which groups absorb there, or filter by class to compare carbonyls, amines, alkynes and more. Every band lists its wavenumber range, intensity, shape and the partner peaks that confirm it.
· Bars run from 4000 cm⁻¹ (left) to 400 cm⁻¹ (right), as on a real spectrum. Darker bars are stronger bands.
| Class | Functional group / vibration | Wavenumber (cm⁻¹) | Intensity / shape | Notes |
|---|---|---|---|---|
| Alkanes | Alkane C–H C–H stretch (sp³) | 2850–3000 | Strong sharp | Almost every organic compound shows peaks just below 3000 cm⁻¹. |
| Alkanes | CH₂ bend C–H bend (scissoring) | 1450–1470 | Medium sharp | ≈1465 cm⁻¹. |
| Alkanes | CH₃ bend C–H bend (umbrella) | 1370–1380 | Medium sharp | ≈1375 cm⁻¹. A gem-dimethyl or isopropyl group splits it into a doublet. |
| Alkenes | Alkene =C–H =C–H stretch (sp²) | 3000–3100 | Medium sharp | Just above 3000 cm⁻¹, which separates it from alkane C–H. |
| Alkenes | Alkene C=C C=C stretch | 1600–1680 | Weak–medium sharp | Weak or absent in symmetric trans or tetrasubstituted alkenes. Conjugation lowers it. |
| Alkenes | Alkene =C–H bend =C–H out-of-plane bend | 650–1000 | Strong sharp | Pattern shows substitution: monosubstituted ≈990 and 910; trans ≈970; 1,1-disubstituted ≈890. |
| Alkynes | Terminal alkyne ≡C–H ≡C–H stretch (sp) | 3260–3330 | Strong sharp | Strong and narrow near 3300 cm⁻¹. Narrower than O–H or N–H. |
| Alkynes | Alkyne C≡C C≡C stretch | 2100–2260 | Weak–medium sharp | Weak. Absent in symmetric internal alkynes. |
| Aromatics | Aromatic C–H C–H stretch (sp²) | 3000–3100 | Weak–medium sharp | Often several small peaks just above 3000 cm⁻¹. |
| Aromatics | Aromatic C=C C=C ring stretch | 1585–1600 | Medium sharp | Usually paired with a band near 1500–1450 cm⁻¹. |
| Aromatics | Aromatic C=C C=C ring stretch | 1450–1500 | Medium sharp | Second ring-stretch band. |
| Aromatics | Aromatic overtones Overtone / combination bands | 1667–2000 | Weak sharp | Weak pattern of bands that reveals the ring substitution pattern. |
| Aromatics | Aromatic C–H bend C–H out-of-plane bend | 690–900 | Strong sharp | Monosubstituted: ≈750 and ≈690; ortho ≈750; para ≈830; meta ≈780 and ≈690 (plus ≈880). |
| Alcohols & phenols | Alcohol O–H (H-bonded) O–H stretch | 3200–3400 | Strong broad | Broad, rounded band in neat liquids and solids. |
| Alcohols & phenols | Alcohol O–H (free) O–H stretch | 3600–3650 | Medium sharp | Only in dilute solution or the gas phase. |
| Alcohols & phenols | Alcohol C–O C–O stretch | 1000–1260 | Strong sharp | 1° ≈1050, 2° ≈1100, 3° ≈1150; phenols ≈1220 cm⁻¹. |
| Ethers | Ether C–O C–O–C stretch | 1000–1300 | Strong sharp | Dialkyl ≈1120. Aryl alkyl ethers show two bands, ≈1250 and ≈1040. No O–H or C=O. |
| Carbonyls | Ketone C=O C=O stretch | 1705–1725 | Strong sharp | Saturated ketone ≈1715 cm⁻¹. Conjugation lowers it to 1685–1666. Ring strain raises it (cyclopentanone ≈1745, cyclobutanone ≈1780). |
| Carbonyls | Aldehyde C=O C=O stretch | 1720–1740 | Strong sharp | Saturated aldehyde ≈1725. Conjugated 1710–1685. |
| Carbonyls | Aldehyde C–H C–H stretch (Fermi doublet) | 2700–2860 | Weak–medium sharp | Two peaks near 2820 and 2720 cm⁻¹. The 2720 band is diagnostic for an aldehyde. |
| Carbonyls | Carboxylic acid O–H O–H stretch | 2400–3400 | Strong very broad | Extremely broad band (H-bonded dimer) that overlaps the C–H stretches. |
| Carbonyls | Carboxylic acid C=O C=O stretch | 1700–1730 | Strong sharp | Dimer ≈1710. Conjugated 1710–1680. |
| Carbonyls | Carboxylic acid C–O C–O stretch | 1210–1320 | Strong sharp | With the broad O–H and C=O, it confirms a carboxylic acid. |
| Carbonyls | Ester C=O C=O stretch | 1735–1750 | Strong sharp | Saturated ester ≈1735. Conjugated or aryl esters 1730–1715. δ-lactone ≈1735, γ-lactone ≈1770. |
| Carbonyls | Ester C–O C–O stretch | 1000–1300 | Strong sharp | Two or more strong bands, "rule of three" with the C=O. |
| Carbonyls | Acid chloride C=O C=O stretch | 1775–1810 | Strong sharp | ≈1800 cm⁻¹: the highest common single carbonyl. |
| Carbonyls | Anhydride C=O C=O stretch (asymmetric) | 1800–1830 | Strong sharp | Anhydrides show two C=O bands about 60 cm⁻¹ apart. |
| Carbonyls | Anhydride C=O C=O stretch (symmetric) | 1740–1775 | Strong sharp | Second anhydride carbonyl band. |
| Carbonyls | Amide C=O (amide I) C=O stretch | 1630–1680 | Strong sharp | Lowest common carbonyl, because N lone-pair resonance weakens the C=O. |
| Amines & amides | Primary amine / amide N–H N–H stretch (two bands) | 3300–3500 | Medium medium | Two spikes (asymmetric + symmetric). Sharper and weaker than O–H. |
| Amines & amides | Secondary amine / amide N–H N–H stretch (one band) | 3300–3350 | Medium medium | One band. Tertiary amines show none. |
| Amines & amides | Amine N–H bend N–H bend (scissoring) | 1560–1640 | Medium medium | Primary amines. Amides show the amide II band at 1640–1550. |
| Amines & amides | Amine C–N C–N stretch | 1000–1350 | Medium sharp | Aliphatic 1250–1000. Aromatic amines 1350–1250. |
| Nitrogen groups | Nitrile C≡N C≡N stretch | 2210–2260 | Medium sharp | Aliphatic ≈2250. Conjugated or aryl 2240–2220. Sharp and medium. |
| Nitrogen groups | Isocyanate N=C=O N=C=O asymmetric stretch | 2240–2275 | Strong broad | Very strong and broad near 2270 cm⁻¹. |
| Nitrogen groups | Azide N=N=N N₃ asymmetric stretch | 2120–2160 | Strong sharp | Strong band about 2100–2160 cm⁻¹. |
| Nitrogen groups | Imine C=N C=N stretch | 1640–1690 | Variable sharp | Variable intensity. |
| Nitrogen groups | Nitro N=O N–O asymmetric stretch | 1515–1560 | Strong sharp | ≈1550. A strong pair with the 1380 band. |
| Nitrogen groups | Nitro N=O N–O symmetric stretch | 1345–1385 | Strong sharp | ≈1380 cm⁻¹. |
| Sulfur & phosphorus | Thiol S–H S–H stretch | 2550–2600 | Weak sharp | Weak but in a clear region. |
| Sulfur & phosphorus | Sulfoxide S=O S=O stretch | 1030–1070 | Strong sharp | ≈1050 cm⁻¹. |
| Sulfur & phosphorus | Sulfone / sulfonyl S=O S=O asymmetric stretch | 1300–1350 | Strong sharp | Paired with the symmetric band at 1160–1120. |
| Sulfur & phosphorus | Sulfone / sulfonyl S=O S=O symmetric stretch | 1120–1160 | Strong sharp | Also seen in sulfonamides and sulfonate esters. |
| Sulfur & phosphorus | Phosphine P–H P–H stretch | 2350–2440 | Medium sharp | Sharp, medium. |
| Sulfur & phosphorus | Phosphoryl P=O P=O stretch | 1140–1300 | Strong sharp | Phosphates and phosphine oxides. |
| Halides | C–F C–F stretch | 1000–1400 | Strong sharp | Very strong. CF₃ gives several strong bands. |
| Halides | C–Cl C–Cl stretch | 540–785 | Strong sharp | Often hidden in the fingerprint region. |
| Halides | C–Br C–Br stretch | 510–650 | Strong sharp | Below most mid-IR scans. |
| Halides | C–I C–I stretch | 485–600 | Strong sharp | Below most mid-IR scans. |
| Cumulenes & others | Allene C=C=C C=C=C asymmetric stretch | 1900–1950 | Medium sharp | ≈1950 cm⁻¹. |
| Cumulenes & others | Carbon dioxide (artifact) O=C=O asymmetric stretch | 2330–2360 | Medium sharp | Atmospheric CO₂ near 2350 cm⁻¹: usually a background artifact, not your sample. |
| Cumulenes & others | Metal carbonyl C≡O C≡O stretch | 1800–2100 | Strong sharp | Terminal M–CO 2100–1850; bridging 1850–1750. |
The four regions of an IR spectrum
| Region (cm⁻¹) | What absorbs there | Look for |
|---|---|---|
| 4000–2500 | Single bonds to hydrogen: O–H, N–H, C–H | Broad O–H (3400, or 3300–2500 for acids), N–H spikes, C–H just above or below 3000 |
| 2500–2000 | Triple bonds and cumulated double bonds | C≡N ≈2250, C≡C ≈2150, N=C=O ≈2270 (and the CO₂ artifact at 2350) |
| 2000–1500 | Double bonds | C=O 1820–1630 (the strongest peak in most spectra), C=C 1680–1600, aromatic 1600/1500 |
| 1500–400 | Fingerprint region: C–O, C–N, C–X stretches and bending modes | Strong C–O 1300–1000. The pattern as a whole is unique to each compound. |
How to read an IR spectrum in five steps
- Check for C=O (1820–1630 cm⁻¹). A strong band here means a carbonyl. Its position sorts it out: acid chloride ≈1800 > anhydride (two bands) > ester ≈1735 > aldehyde ≈1725 > ketone ≈1715 ≈ acid ≈1710 > amide ≈1650.
- If there is a C=O, look for partners. A very broad O–H from 3300–2500 means a carboxylic acid. Two weak bands at 2820/2720 mean an aldehyde. Strong C–O at 1300–1000 means an ester. N–H at 3500–3300 means an amide.
- No C=O? Check 3600–3200. A broad, rounded band means an alcohol or phenol. One or two sharper spikes mean an amine (N–H). A strong, narrow band at 3300 means a terminal alkyne.
- Check 3000 cm⁻¹. Peaks just above 3000 mean sp² or sp C–H (alkene or aromatic). Peaks just below mean sp³ C–H. For aromatics, confirm with the 1600/1500 pair and strong out-of-plane bends at 900–690.
- Check 2300–2100 for nitriles and alkynes, then use the degree of unsaturation to make sure the rings and π bonds add up.
Why carbonyl positions differ
The C=O frequency follows bond strength. Electron-withdrawing groups such as Cl and the second C=O of an anhydride strengthen the double bond and push it higher. Resonance donation from N (amides) or conjugation with C=C or an aromatic ring gives the bond more single-bond character, lowering the frequency by about 25–40 cm⁻¹. Ring strain raises it: cyclohexanone ≈1715, cyclopentanone ≈1745, cyclobutanone ≈1780.
Sources: typical ranges compiled from D. L. Pavia, G. M. Lampman, G. S. Kriz & J. R. Vyvyan, Introduction to Spectroscopy, 5th ed. (Cengage, 2015), and R. M. Silverstein, F. X. Webster, D. J. Kiemle & D. L. Bryce, Spectrometric Identification of Organic Compounds, 8th ed. (Wiley, 2014). Exact positions shift with phase, solvent, hydrogen bonding and conjugation, so always confirm with partner bands.
Drawing structures for your notes? MolDraw is a free online chemical structure editor for molecules, reactions and lab diagrams.
Open MolDraw editorFrequently asked questions
Where is the C=O peak in IR?
Between about 1820 and 1630 cm⁻¹, usually the strongest peak in the spectrum. A saturated ketone absorbs at ≈1715, an ester at ≈1735, an aldehyde at ≈1725, an acid chloride at ≈1800 and an amide at ≈1650 cm⁻¹.
How do you tell an alcohol O–H from a carboxylic acid O–H?
An alcohol O–H is a broad, rounded band at 3400–3200 cm⁻¹. A carboxylic acid O–H is much broader, spreading from about 3300 to 2500 cm⁻¹ over the C–H peaks, and it comes with a C=O near 1710 cm⁻¹.
What does a peak at 3300 cm⁻¹ mean?
It could be an O–H (broad), an N–H (medium, one or two spikes) or a terminal alkyne ≡C–H (strong and very narrow). The shape tells them apart. Enter 3300 in the peak finder to see all the options.
What is the fingerprint region?
The region below about 1500 cm⁻¹, where many bending and skeletal vibrations overlap. It is hard to assign peak by peak, but the overall pattern is unique to each compound, so it is used to match against reference spectra.
Why is there a peak at 2350 cm⁻¹ in my spectrum?
Almost always it is atmospheric carbon dioxide that was not fully subtracted in the background scan, not a band from your sample.
How do I tell a primary from a secondary amine by IR?
Primary amines (R–NH₂) show two N–H stretching bands near 3400 and 3300 cm⁻¹. Secondary amines show one. Tertiary amines show none.
What does wavenumber mean?
Wavenumber (cm⁻¹) is 1/wavelength, which is proportional to energy and frequency. Stronger bonds and lighter atoms vibrate at higher wavenumbers.