What absorbs at 1402 cm⁻¹ in an FTIR spectrum?
A band near 1402 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 1402 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 |
|---|---|---|---|
| Alkyl C-H | 10 | 8 | 1.0 |
| Acetate | 8 | 7 | 1.0 |
| Carboxyl (COOH) | 7 | 6 | 1.0 |
| Methoxy (OCH3) | 7 | 6 | 1.0 |
| Methacrylate | 7 | 6 | 1.0 |
| C-O single bond | 6 | 5 | 1.0 |
| Amide | 5 | 4 | 1.0 |
| Aromatic ring | 4 | 4 | 1.0 |
| Hydroxyl (O-H) | 3 | 2 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| N h | 2 | 2 | 1.0 |
| Carbonyl (C=O) | 2 | 1 | 1.0 |
| Alkene (C=C) | 2 | 1 | 1.0 |
| Fluorine (C-F) | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Nitrate | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Sulfonate | 1 | 1 | 1.0 |
| S eq o | 1 | 1 | 1.0 |
| Sulfonyl | 1 | 1 | 0.7 |
| Ketone | 1 | 0 | 1.0 |
| Ester | 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 |
|---|---|---|---|
| ZnS | 1402, 1650, 1116 | Alkyl C-H, Acetate, Carboxyl (COOH) | 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 1402 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
-
Carboxyl (COOH) confidence 1.0
“In all compositions of cm-1 Zn1-xInxS nanoparticles, a medium peak ~ 1402 can correspond to C = O stretching mode for the carboxylic group (-COOH) of zinc acetate [34].”
In-doped ZnS nanoparticles: structural, morphological, optical and antibacterial properties DOI: 10.1007/s00339-021-04425-9 -
Amide confidence 1.0
“Amide I 1543.15 ± 4.01 1543.01 ± 0.00 N-H deformation and C-N stretching Amide II -COOstretching Pectin 1401.56 ± 1.11 1402.21 ± 0.00”
Changes in chemical composition and structure of root cell wall of citrus rootstock seedlings in response to boron deficiency by FTIR spectroscopy DOI: 10.1080/14620316.2017.1362327 -
S eq o confidence 1.0
“Summary of molecular vibration of PBS chromophore (cm-1) Group Wavenumber, 𝝂 700 C-H bending 754 C-H bending of 776 C-H bending 1079 S=O stretching Pre-pro 1218 C-N stretching 1289 C-N stretching 1330 S=O stretching 1402 S=O stretching 1427”
Power-Dependent Nonlinear Optical Behaviours of Ponceau BS Chromophore at 532 nm via Z-Scan Technique DOI: 10.1016/j.jphotochem.2020.112574 -
Hydroxyl (O-H) confidence 1.0
“cm-1 at 3378 for the stretching vibration of O-H groups was observed in the spectrum of FA, and the cc cm-1 cm-1 peaks located at 1402 were its bending vibrations.”
Microencapsulated Soil Conditioner with a Water-Soluble Core: Improving Soil Nutrition of Crop Root DOI: 10.1080/02652048.2020.1836056 -
Carbonate confidence 1.0
“Organic Components Azurite was identified in sample K-4 by the carbonate ν3 stretch at 1461 and 1402 cm-1 2.3.1.”
New Insights into the Medieval Hispano-Muslim Panel Painting: The Alfarje Found in a Balearic Casal (Spain) DOI: 10.3390/molecules28031235 -
Alkyl C-H confidence 1.0
“Moreover, the ~1402 band can be mainly assigned to the CH bending vibration of 3 (PC)16.”
Ami 等 - 2016 - In situ characterization of protein aggregates in DOI: 10.1038/srep29096 -
Alkyl C-H confidence 1.0
“cm-1 The peak at 1402 represents CH symmetric 1315 amino Peaks at 1105 3 carbohydrates77,”
El-Naggar 等 - 2022 - Statistical optimization for simultaneous removal DOI: 10.1038/s41598-022-11069-z -
Nitrate confidence 1.0
“In addition, the adsorption band at 1402 is attributed to cm-1, cm-1, cm-1 the stretching vibrations of nitrate anions.”
Design and preparation of nanoarchitectonics of LDH/polymer composite with particular morphology as catalyst for green synthesis of imidazole derivatives DOI: 10.1038/s41598-022-15582-z
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