What absorbs at 3345 cm⁻¹ in an FTIR spectrum?
A band near 3345 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 3345 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) | 11 | 11 | 1.0 |
| N h | 4 | 4 | 1.0 |
| Alkyl C-H | 2 | 2 | 1.0 |
| N n bond | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 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 |
|---|---|---|---|
| polypropylene | 3345, 1030, 1600 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| PLA | 3345, 1650, 1073 | Alkyl C-H, Hydroxyl (O-H) | 1 |
| hydroxyapatite | 3345, 1620, 1639 | Hydroxyl (O-H), Alkyl C-H | 1 |
| rGO | 3345, 2358, 2930 | Hydroxyl (O-H), Alkyl C-H, N h | 1 |
| hydrogels | 3345, 3281, 1700 | 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 3345 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
-
Water (H2O) confidence 1.0
“- - 3430 3410 3393 3393 3374 3430 Alcohols / O-H strong & 3374 3374 3374 3374 3374 water stretching broad - - 3345 - - - - 3336 - - - - - 2961 2961 -”
Azlah 等 - 2020 - A fast and reliable 2D-IR spectroscopic technique DOI: 10.1016/j.vibspec.2019.103014 -
Hydrogen bond confidence 1.0
“The cm-1 obtained FTIR spectra show the presence of the strong bands near at 3345 that corresponds to hydrogen bonds of -NH group along with sharp absorption cm-1 bands at 2924 and 2854 that are related to symmetric and asymmetric -CH 2”
Preparation and characterization of aliphatic polyurethane and modified hydroxyapatite composites for bone tissue engineering DOI: 10.1007/s00289-019-03067-5 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Lueder 等 - 2023 - A framework for quantitative in situ evaluation of DOI: 10.5194/ejm-35-243-2023 -
Hydroxyl (O-H) confidence 1.0
“cm-1, cm-1, aromatic stretch at 1658 OH stretch at 3345 and To investigate the diffusion coefficient of the hydrogels, a”
Owonubi 等 - 2018 - Characterization and in vitro release kinetics of DOI: 10.1007/s40090-018-0139-2 -
confidence 1.0
“Fourier Transform Spectroscopy BAB in the pure drug spectrum exhibits the characteristics peaks at 3345 cm-1, 3012 cm-1, 2654 cm-1, and 2322 cm-1 for the N-H stretching, aromatic = C-H stretching, -C-H”
Design and Characterization of Baricitinib Incorporated PLA 3D Printed Pills by Fused Deposition Modeling: An Oral Pill for Treating Alopecia Areata DOI: 10.3390/polym15081825 -
confidence 1.0
“sin2 1.83 N-H bend 1184 131 N-H(cid:5)(cid:5)(cid:5) stretching 3293 249 N-H stretching 3345”
Ay 和 Aydinli - 2004 - Comparative investigation of hydrogen bonding in s DOI: 10.1016/j.optmat.2003.12.004 -
Hydroxyl (O-H) confidence 1.0
“(cm-1) Band Band Assignment 3345 O-H stretching 2958”
Quantification of the Geranium Essential Oil, Palmarosa Essential Oil and Phenylethyl Alcohol in Rosa damascena Essential Oil Using ATR-FTIR Spectroscopy Combined with Chemometrics DOI: 10.3390/foods10081848 -
Hydroxyl (O-H) confidence 1.0
“A strong broad cm-1, peak is seen at 3345 which has been assigned to various O-H stretching vibrations, cm-1 while at 2919 a characteristic peak is related to the asymmetric and symmetric methyl cm-1 and methylene stretching vibrations grou”
Cresnar 等 - 2021 - Insight into the Surface Properties of Wood Fiber- DOI: 10.3390/polym13101535
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