What absorbs at 3309 cm⁻¹ in an FTIR spectrum?
A band near 3309 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 3309 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) | 7 | 7 | 1.0 |
| N h | 7 | 7 | 1.0 |
| Amide | 4 | 4 | 1.0 |
| Alkyl C-H | 3 | 3 | 1.0 |
| Methacrylate | 2 | 2 | 1.0 |
| Acetate | 2 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| N-O bond | 2 | 2 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 0.9 |
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 |
|---|---|---|---|
| sodium alginate | 3309, 1636, 1080 | Hydroxyl (O-H), Alkyl C-H, Amide | 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 3309 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
-
Hydroxyl (O-H) confidence 1.0
“While in this measurement, the main OH bands around 3309, cm-1 3397, 3526, 3560, and 3610 remained distinguishable at cm-1 high temperatures, except that the weak peak around 3610”
In-situ high-temperature vibrational spectra for synthetic and natural clinohumite: Implications for dense hydrous magnesium silicates in subduction zones DOI: 10.2138/am-2019-6604 -
Amide confidence 1.0
“at surface proved to be HA3-FIB4/Ti, where actin and vinculin patamide II, 1243cm-1 (∼1240) terns are similar to the cells grown in standard conditions and amide I, amide III, and strong absorption band ∼3309cm-1, on bare Ti (Fig.”
Composite biocompatible hydroxyapatite⠍silk fibroin coatings for medical implants obtained by Matrix Assisted Pulsed Laser Evaporation DOI: 10.1016/j.mseb.2009.10.004 -
confidence 1.0
“Before heating, the FTIR spectra showed only the cm-1 cm-1 cm-1 while the side peaks at 3232 and 3185 start to appear after heating peak at 3309 cm-1-series peaks were assigned as -Ti-OH stretching.”
Phlayrahan 等 - 2018 - Fe oxidation state in heat-treated basaltic blue s DOI: 10.1088/1742-6596/1144/1/012057 -
Hydroxyl (O-H) confidence 1.0
“spectroscopy (XAS) was employed to confi rm that the Ti oxidation state was The heat experiment conditions 1650oC were set at 800, 1200, and to investigate the transformation of the -OH vibration in the FTIR spectra of 3309-cm-1 ruby sample”
Phlayrahan 等 - 2018 - Role of Ti Content on the Occurrence of the 3309-c DOI: 10.1007/s10812-018-0662-0 -
Alkyl C-H confidence 1.0
“The spectrum of porous graphene nanosheets is represented by the peaks at 809 cm-1, 1636 cm-1, 2344 cm-1 and 3309 cm-1, resulting from C-H bonding, C=C conjugation, C-N band and N-H extending vibrations.”
An Amperometric Acetylcholine Biosensor Based on Co-Immobilization of Enzyme Nanoparticles onto Nanocomposite DOI: 10.3390/bios13030386 -
confidence 1.0
“These peaks formed owing to the N-H stretching vibration of the primary amine (3309 cm-1), C-H stretching of the alkane groups (2925, 2852 cm-1), stretching of the C=C group (1643 cm-1), O-H bending of carboxylic (1400 cm-1), strong stretch”
Preparation and Physiochemical Characterization of Bitter Orange Oil Loaded Sodium Alginate and Casein Based Edible Films DOI: 10.3390/polym14183855 -
Hydroxyl (O-H) confidence 1.0
“3.1 UV VIS studies of platinum nanoparticles and 387 The strong absorption peak that appeared at 3309 cm-1 is related to O-H stretching (intramolecular hydroUV-vis gen bonded OH).”
Evaluation of biological synthesized platinum nanoparticles using Ononidis radix extract on the cell lung carcinoma A549 DOI: 10.1007/s10544-019-0424-7 -
confidence 1.0
“cm-1 vibration in ethanol shows a peak at 3308.63 with transmittance 75.97 % while N-H stretching cm-1 cm-1 vibration in benzylamine show two peaks at 3371.10 and 3284.83 corresponding to symmetric Page 6/29 and asymmetric (higher frequency”
Hema 等 - 2022 - Structural and vibrational study of molecular inte DOI: 10.21203/rs.3.rs-649250/v1
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