What absorbs at 3320 cm⁻¹ in an FTIR spectrum?
A band near 3320 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 3320 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 |
|---|---|---|---|
| Hydroxyl (O-H) | 16 | 16 | 1.0 |
| N h | 12 | 11 | 1.0 |
| Secondary amine | 6 | 5 | 1.0 |
| Alkyl C-H | 4 | 4 | 1.0 |
| Water (H2O) | 3 | 3 | 1.0 |
| Carbonyl (C=O) | 3 | 3 | 1.0 |
| Amide | 3 | 2 | 1.0 |
| Carbohydrate | 2 | 2 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Methacrylate | 1 | 1 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Acetate | 1 | 1 | 1.0 |
| Urethane | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Chlorine | 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 | 3320, 1650, 1655 | Alkyl C-H, Hydroxyl (O-H), N h | 1 |
| polypropylene | 3320, 1030, 1600 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| polyurethane | 3320, 2270, 1700 | Alkyl C-H, N h | 1 |
| bio-based | 3320, 1720, 1740 | Hydroxyl (O-H), N h | 1 |
| silver nanoparticles | 3320, 1636, 1631 | Hydroxyl (O-H), Alkyl C-H, N h | 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 3320 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
-
C c single bond confidence 1.0
“5 (control), C-C is evident at 1588 The appearance cm-1 exposed the available functional moieties at the of a broader peak at 3320 refers to the”
Hernandez-Vargas 等 - 2020 - Development and Characterization of Nanoparticles- DOI: 10.22207/JPAM.14.4.11 -
Hydroxyl (O-H) confidence 1.0
“However, 3360cm-1 created by the incorporation of trivalent cations, as previonly OH bands at 3320 and have been identified 3270cm-1 Al3+ Mg2+, ously proposed by Hill (1968).”
Lueder 等 - 2023 - A framework for quantitative in situ evaluation of DOI: 10.5194/ejm-35-243-2023 -
confidence 1.0
“The spectra of the N-H stretching cm-1 region (Figure 2a) show a strong absorption band centered on 3320 that corresponds to the hydrogen bonding of NH to carbonyl groups [22,24].”
Effects of NCO/OH Ratios on Bio-Based Polyurethane Film Properties Made from Acacia mangium Liquefied Wood DOI: 10.3390/polym15051154 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Sahudin 等 - 2022 - Enhancement of Skin Permeation and Penetration of DOI: 10.3390/cosmetics9060114 -
confidence 1.0
“The positions of the new bands are at 3361 cm-1 located at 3328 cm-1 in Fe-containing samples, at 3283 and for Cr, and at 3381 and 3320 cm-1 for Al.”
Stalder - 2004 - Influence of Fe, Cr and Al on hydrogen incorporati DOI: 10.1127/0935-1221/2004/0016-0703 -
N h confidence 1.0
“cm-1 The main region interested in they study are -NH absorption peak at 3320 was due to hydrogen bonded -NH groups of urethane linkages.”
Suryani 和 Zaimahwati - 2014 - Fourrier Transform Infrared and Gel Permeation Chr DOI: 10.4028/www.scientific.net/AMM.525.162 -
Amide confidence 1.0
“The spectrum for collagen configuration then shows a conspicuous increase in absorptions for amide A and Nativeratandcodskincollagens 1630(shoulder)- (cid:2)3320cm-1 (cid:2)3020cm-1 B, (-OH) and (NH stretching) at rates of 1656(centralpeak)”
Vidal 和 Mello - 2011 - Collagen type I amide I band infrared spectroscopy DOI: 10.1016/j.micron.2010.09.010 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Physical and Chemical Characteristics of Agricultural-Plastic Wastes for Feasibility of Solid Fuel Briquette Production DOI: 10.3390/su142315751
Have a spectrum with this band?
Upload your FTIR spectrum and get a full interpretation report — peak assignments with literature citations, library matches, and a literature-backed analysis — in seconds.