What absorbs at 1320 cm⁻¹ in an FTIR spectrum?
A band near 1320 cm⁻¹ can point to several functional groups. Below are the most likely assignments, ranked by how much published evidence supports each — every one traceable to literature (DOI) and cross-validated against our 130,000+ reference spectra and knowledge graph.
Backed by 8 cited sources
Quick answer
A band near 1320 cm⁻¹ is usually interpreted by checking which functional groups repeatedly co-occur there in the literature, then confirming at least one or two additional peaks in the same sample. This page ranks those assignments by accumulated evidence rather than by a single fixed textbook rule.
Possible functional-group assignments
| Functional group | Supporting facts | Cited sources | Top confidence |
|---|---|---|---|
| C-O single bond | 25 | 24 | 1.0 |
| Acetate | 23 | 23 | 1.0 |
| Methacrylate | 22 | 22 | 1.0 |
| Methoxy (OCH3) | 21 | 21 | 1.0 |
| Amide | 17 | 17 | 1.0 |
| Alkyl C-H | 7 | 7 | 1.0 |
| Carbohydrate | 7 | 7 | 1.0 |
| Hydroxyl (O-H) | 7 | 6 | 1.0 |
| Aromatic ring | 6 | 6 | 1.0 |
| Secondary amine | 5 | 5 | 1.0 |
| C n single bond | 5 | 5 | 1.0 |
| Ring structure | 4 | 4 | 1.0 |
| Ester | 4 | 4 | 1.0 |
| Lignin | 3 | 3 | 1.0 |
| Carbonyl (C=O) | 3 | 3 | 1.0 |
| Carboxyl (COOH) | 3 | 3 | 1.0 |
| Phosphate (PO4) | 3 | 1 | 1.0 |
| Ketone | 2 | 2 | 1.0 |
| Acetyl | 2 | 2 | 1.0 |
| Protein alpha helix | 2 | 2 | 1.0 |
| Borate | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| S eq o | 1 | 1 | 1.0 |
| Sulfonyl | 1 | 1 | 1.0 |
| Adsorbed carbon monoxide | 1 | 1 | 1.0 |
| Nucleic acid | 1 | 1 | 1.0 |
| Boron nitrogen | 1 | 1 | 0.9 |
| Nitrate | 1 | 1 | 0.9 |
| Sulfur heterocycle | 1 | 1 | 0.8 |
| Phosphorus | 1 | 0 | 1.0 |
Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.
Possible materials
| Material | Supporting peaks | Overlapping groups | Cited sources |
|---|---|---|---|
| chitosan | 1320, 1650, 1655 | Acetate, Methacrylate, C-O single bond | 1 |
| polysaccharide | 1320, 1637, 1064 | Methacrylate, Acetate, C-O single bond | 1 |
Materials are shown only when the same literature pool supports this band and at least one additional characteristic peak.
Spectrum logic
This band becomes meaningful only when read with its neighboring peaks. In practice, analysts first look at the assignments above, then check whether the same sample also shows other peaks expected for the same structural motif. A lone band near 1320 cm⁻¹ is usually not enough for material identification by itself.
Real-world usage
This type of query is common in polymer identification, unknown plastic screening, QC troubleshooting, recycled-material verification, and literature-backed peak assignment review.
Common mistakes
- Treating one isolated band as proof of a material without checking at least one or two supporting peaks.
- Ignoring overlap: multiple functional groups can contribute near the same wavenumber.
- Skipping validation when additives, blends, oxidation, or contamination may distort the spectrum.
Verification advice
When ambiguity remains, validate the hypothesis with DSC, GC-MS, or TGA, especially for blends, degraded samples, and filled polymers.
Literature behind these assignments
-
Carbohydrate confidence 1.0
“Fourier transform infrared (FTIR) peak at 1507 confirmed the presence of lignin and the cm-1 appearance of three new peaks at 1320, 1416, and 1595 showed successful attachment of carboxymethyl group onto the cellulose backbone.”
Cellulose-based polymer electrolyte derived from waste coconut husk: residual lignin as a natural plasticizer DOI: 10.1007/s10965-020-02110-8 -
Nucleic acid confidence 1.0
“It was found that with the increase of NaCl, MgCl 2, or ethanol concentration in the incm-1, cm-1, cm-1 duction solution, the characteristic Z-DNA peaks of 1320 1125 and 925 in the infrared spectra changed during the B-Z DNA transition, and”
Assessing B-Z DNA Transitions in Solutions via Infrared Spectroscopy DOI: 10.3390/biom13060964 -
Amide confidence 1.0
“cm(cid:1)1 The peak in 1320 correspond to the characteristic band of subjected, because each DTG peak, at any temperature gives the rate of amide group (-OH, -NH2, -CO).”
A comparison of chitosan properties after extraction from shrimp shells by diluted and concentrated acids DOI: 10.1016/j.heliyon.2020.e03486 -
confidence 1.0
“Band intensity of the formate species with a symmetric O-C-O vibration around Adsorbed CO 1320cm(cid:2)1 remains unchanged with increase of methanol concentration from 0.04M to 1M, while the Formate 4.Theresultsuggestsaminor peakcurrentofme”
Kunimatsu 等 - 2009 - Role of adsorbed species in methanol oxidation on DOI: 10.1016/j.jelechem.2009.04.004 -
Acetate confidence 1.0
“The The band band at at about about 1320 1320 cm1 cm1 has has been been assigned assigned to to C-O-H C-O-H bending bending and and CH2 CH2 deformation deformation 14 14 Itcan Itcan be be concluded concluded that that bands in the region 1”
Liu 等 - 2006 - Characterization of the basidiomycetes Thelephora DOI: 10.1117/12.710905 -
Acetate confidence 1.0
“and C-O stretching is seen at 1320”
Synthesis of Aloevera/Acrylonitrile based Nanoparticles for targeted drug delivery of 5-Aminosalicylic acid DOI: 10.1016/j.ijbiomac.2017.08.085 -
Protein alpha helix confidence 1.0
“The position of α-helix in Amide III region is assigned to 1320 cm-1 cm-1 while a turn is recognized at about 1270-1285 (between 1260-1280 in literature [24]).”
Milosevic 等 - 2020 - Exploring the potential of infrared spectroscopy i DOI: 10.1016/j.saa.2019.117882 -
Protein alpha helix confidence 1.0
“cmK1 cmK1 Surprisingly, the Amide 111 band at 1320 showing that egg albumen was showed structure at 960 a-helix substantially denatured (Howell & Li-Chan, 1996), whilst significant but lower values in in high pressure0.27G0.02 no peaks were”
Ngarize 等 - 2005 - A comparative study of heat and high pressure indu DOI: 10.1016/j.foodhyd.2004.12.008
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