What absorbs at 402 cm⁻¹ in an FTIR spectrum?
A band near 402 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 402 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 |
|---|---|---|---|
| N h | 6 | 5 | 1.0 |
| Secondary amine | 5 | 5 | 1.0 |
| Ammonium | 3 | 3 | 1.0 |
| N-O bond | 3 | 1 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| Amide | 2 | 2 | 1.0 |
| Quaternary ammonium | 2 | 2 | 1.0 |
| Carboxyl (COOH) | 1 | 1 | 1.0 |
| Bronsted acid site | 1 | 1 | 1.0 |
| Bromine | 1 | 1 | 1.0 |
| Chlorine | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Nitrate | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 0 | 1.0 |
| N n bond | 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 |
|---|---|---|---|
| PET | 402, 1408, 800 | N h | 1 |
| polydopamine | 402, 1543, 1707 | 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 402 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
-
confidence 1.0
“The ESCA spectrum of treated PET revealed that the surface chemistry obtained after plasma polymerizing TFE was one clearly dominated by CF and CF moieties, 2 asdemonstratedbythelargepeaksappearingat291.1and289.5eV,respectively.Asexpected,s”
Cohn 和 Stern - 2000 - Sequential surface derivatization of PET films DOI: 10.1021/ma9900784 -
Carbonate confidence 1.0
“luted peak at 402 eV could be assigned to the in the quaternary Regarding the effect of bicarbonate on nitrate removal, similar findings ammonium species, which are involved in the electrostatic attraction of were reported in the literature”
Kang 和 Kim - 2020 - Synthesis of quaternized mesoporous silica SBA-15 DOI: 10.1016/j.micromeso.2019.109967 -
N h confidence 1.0
“It can be seen from Figure 2a that the peak at 401.6 eV represents NH in the MEL and the peak at 399.3 eV may stand for the nitrogen in the 2 C=N”
Liang 等 - 2020 - Thermal Kinetics of a Lignin-Based Flame Retardant DOI: 10.3390/polym12092123 -
Quaternary ammonium confidence 1.0
“Simon Christian aMBIE The Biocide Toolbox Programme, The University of Auckland, Private Bag 92019, Auckland 1042, New Zealand bSchool of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland 1042, New Zealand cDepartme”
Anchored quaternary ammonium salts adsorbed on polyurethane film surfaces DOI: 10.1016/j.porgcoat.2019.105343 -
Amine primary confidence 1.0
“The N 1s peak emerged in the GO-PDA spectra was deconvoluted and fitted into three main peaks at binding energies of 402, 399, and 396 eV corresponding to primary amine”
Polydopamine Functionalized Graphene Oxide as Membrane Nanofiller: Spectral and Structural Studies DOI: 10.3390/membranes11020086 -
C-O single bond confidence 1.0
“Among 401 cm-1 them, the absorption at 1044 was mainly attributed to C-O stretching on C-O-C 402”
Beltramino 等 - 2016 - Optimization of sulfuric acid hydrolysis condition DOI: 10.1007/s10570-016-0897-y -
Quaternary ammonium confidence 1.0
“NeSc ]C, [50], while the other two peaks at 398.8eV for N(C, H) 1468cm-1, CeH which is assigned to asymmetric bend in new peak at and 401.72eV, which are associated to the overlapped with Ntert N+ (in quaternary ammonium salt).”
Quaternization of algal/PEI beads (a new sorbent): Characterization and application to scandium sorption from aqueous solutions DOI: 10.1016/j.cej.2019.123210 -
Amide confidence 1.0
“The peak at 402 eV is associated with C-N linkages suggesting that during the plasma treatment new covalent bonds between”
Kaklamani 等 - 2010 - Effect of plasma surface modification on the bioco DOI: 10.1088/1748-6041/5/5/054102
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.