What absorbs at 1634 cm⁻¹ in an FTIR spectrum?
A band near 1634 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 1634 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 |
|---|---|---|---|
| Amide | 31 | 29 | 1.0 |
| Hydroxyl (O-H) | 20 | 19 | 1.0 |
| Carbonyl (C=O) | 20 | 18 | 1.0 |
| Water (H2O) | 13 | 13 | 1.0 |
| Methacrylate | 13 | 13 | 1.0 |
| Carboxyl (COOH) | 13 | 13 | 1.0 |
| Acetate | 12 | 12 | 1.0 |
| Alkene (C=C) | 9 | 9 | 1.0 |
| Alkyl C-H | 9 | 9 | 1.0 |
| Ketone | 9 | 9 | 1.0 |
| Ester | 9 | 9 | 1.0 |
| N h | 8 | 8 | 1.0 |
| Protein beta sheet | 8 | 6 | 1.0 |
| Aromatic ring | 5 | 5 | 1.0 |
| Protein | 4 | 4 | 1.0 |
| Secondary amine | 4 | 4 | 1.0 |
| Metal oxygen | 4 | 3 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| C=n | 2 | 2 | 1.0 |
| C n single bond | 2 | 2 | 1.0 |
| Ring structure | 2 | 2 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Protein alpha helix | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Nucleic acid | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| N c o | 1 | 1 | 1.0 |
| Urea | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Nitro (NO2) | 1 | 1 | 1.0 |
| Carbon dioxide | 1 | 1 | 1.0 |
| Aldehyde (CHO) | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| N-O bond | 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 |
|---|---|---|---|
| PMMA | 1634, 1722, 1383 | Carbonyl (C=O) | 1 |
| silica | 1634, 1100, 1080 | Hydroxyl (O-H) | 1 |
| chitosan | 1634, 1650, 1655 | Amide, Hydroxyl (O-H) | 1 |
| epoxy | 1634, 1660, 1735 | Amide, Carbonyl (C=O) | 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 1634 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
-
Alkene (C=C) confidence 1.0
“LLM confirmed rule peak-group candidate”
Ashri 等 - 2018 - Modified Dioscorea hispida starch-based hydrogels DOI: 10.1016/j.ijbiomac.2017.10.125 -
Alkene (C=C) confidence 1.0
“35 36 cm-1 The twin weak absorption bands at 1634 and 1613 are from C=C stretching vibration while the 37 cm-1 38 absorbances at 2847 and 2940 are attributed to the stretching vibration of aliphatic C-H groups.”
Ataei 等 - 2020 - Electrosprayed PMMA microcapsules containing green DOI: 10.1088/1361-665X/ab9754 -
Amide confidence 1.0
“15 cm-1 V ) of the 1 states of the two acetyl end peaks at 1664 and The peak at 1634 originates from the amide-I stretching carbonyl,13Cd cm-1 1688 mode of the N-methylamino (isotopically labeled are 800 fs and 1 ps, respectively.”
Bagchi 等 - 2007 - Two-dimensional infrared investigation of N-acetyl DOI: 10.1021/jp067348m -
Water (H2O) confidence 1.0
“Disappearance of strong water absorption (saccharide structure of chitosan) cm21 cm21 band at 1634 enables the visibility of peak at 1547 CAH 891 Wagging of NH1 which corresponds to the symmetric stretching of .”
Mechanism and Kinetics of Curing of Diglycidyl Ether of Bisphenol A (DGEBA) Resin by Chitosan DOI: 10.1002/pen.24463 -
Aromatic ring confidence 1.0
“A pointing peak 326 cm-1 cm-1 at 1510 could be due to aromatic ring vibrations of lignin [35], and peak at 1634 327”
Balan 等 - 2021 - Esterification of residual palm oil using solid ac DOI: 10.1016/j.jtice.2012.07.001. -
Hydroxyl (O-H) confidence 1.0
“at 3516, 3429 and 3433 attributed to hydroxyl ( OH) appear cm-1 and the peaks appear at 1634, 1634 and 1632 corresponding Table 2 Table 1 crystallite structure parameters of samples.”
AC impedance investigation and charge–discharge performance of NaOH surface-modified natural graphite DOI: 10.1016/j.electacta.2013.03.138 -
Hydroxyl (O-H) confidence 1.0
“The peak at 1634 denote the characteristic H-O-H bond vibration of water molecule.”
Green synthesis and characterization of UKMRC-8 rice husk-derived mesoporous silica nanoparticle for agricultural application DOI: 10.1038/s41598-022-24484-z -
Acetate confidence 1.0
“According to the Lambert-Beer law, the is likely due to -C-O stretching stretch B1634 (d(-OH)).43,44 cm(cid:2)1 as(-COO(cid:2)) n absorbance of the and -OH deformation vibration The peak at band at is linearly cm(cid:2)1 (n(-C-O)).45 1307 p”
Gao 等 - 2018 - A kinetics study of the heterogeneous reaction of DOI: 10.1039/c8cp01914b
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