What absorbs at 1629 cm⁻¹ in an FTIR spectrum?
A band near 1629 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 1629 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 |
|---|---|---|---|
| Carbonyl (C=O) | 14 | 13 | 1.0 |
| Amide | 12 | 10 | 1.0 |
| Methacrylate | 9 | 8 | 1.0 |
| Carboxyl (COOH) | 9 | 8 | 1.0 |
| Acetate | 9 | 8 | 1.0 |
| Protein beta sheet | 8 | 8 | 1.0 |
| Water (H2O) | 8 | 6 | 1.0 |
| N h | 7 | 6 | 1.0 |
| Alkene (C=C) | 6 | 6 | 1.0 |
| Ketone | 6 | 5 | 1.0 |
| Ester | 6 | 5 | 1.0 |
| Hydroxyl (O-H) | 6 | 5 | 1.0 |
| Alkyl C-H | 4 | 3 | 1.0 |
| Secondary amine | 3 | 3 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| Aromatic ring | 3 | 3 | 1.0 |
| Silicon-oxygen (Si-O) | 3 | 3 | 1.0 |
| C c single bond | 3 | 3 | 1.0 |
| Protein | 3 | 3 | 1.0 |
| Ring structure | 3 | 2 | 1.0 |
| Siloxane (Si-O-Si) | 2 | 2 | 1.0 |
| Nitrogen heterocycle | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Protein beta turn | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Amino acid | 1 | 1 | 1.0 |
| Metal oxygen | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Nucleic acid | 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 |
|---|---|---|---|
| Chitosan | 1629, 1650, 1655 | Amide, Methacrylate | 1 |
| TiO2 | 1629, 1700, 1093 | Methacrylate, 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 1629 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
-
Protein confidence 1.0
“The FT-IR pattern indicated sharp peaks formed around 1628.98 and 1629.28 HaloarchaeaHalolamina which confirmed the presence of the carbonyl group (C=O) on amides and related to proteins, which spp.Molecules2022,27,7366.”
Characterization of Polyhydroxybutyrate, PHB, Synthesized by Newly Isolated Haloarchaea Halolamina spp. DOI: 10.3390/molecules27217366 -
Alkene (C=C) confidence 1.0
“bending at peak 1629 While for the C=C stretching vibration for alkene was observed at peak 1585 cm-1 cm-1 and 1340 indicated to C=C (aromatic) and asymmetric stretching of N=O (NO 2) Strong peak at 1499 group.”
Synthesis and characterization of Heck-cross coupling 4-(4-nitrostyryl) aniline as potential precursor in Schiff-base synthesis DOI: 10.1063/1.5002293 -
Carbohydrate confidence 1.0
“Compared with cm-1 D-glucose, the FT-IR spectrum of the aminated glucose showed a moderate peak at 1629~1608 which was attributed to δ vibration, suggesting glucose reacted to ethylenediamine (en).”
Liao 等 - 2011 - Synthesis and Characterization of an Aminated D-gl DOI: 10.4028/www.scientific.net/AMR.197-198.65 -
Metal oxygen confidence 1.0
“From the TiO2 spectrum, several peaks at 467 cm-1, 1345 cm-1, 1629 cm-1, and 3396 cm-1 can be observed.”
Influence of Sputtering Temperature of TiO2 Deposited onto Reduced Graphene Oxide Nanosheet as Efficient Photoanodes in Dye-Sensitized Solar Cells DOI: 10.3390/molecules25204852 -
Carboxyl (COOH) confidence 1.0
“and 1259 and also a loss of intensity near 1629 comparisonsbetweenmodelandFTIRdata,asuitableFTIR cm-1 It should be noted that the 1629 IR band of fulvic acid peak is required to estimate spectroscopically the amount cm-1 (Figure 6) and the”
Lumsdon 和 Fraser - 2005 - Infrared spectroscopic evidence supporting heterog DOI: 10.1021/es050180iCCC -
Hydroxyl (O-H) confidence 1.0
“cm-1 cm-1 characteristic peak at 1629 and 1639 (amide I) in is correlated with the presence of hydroxyl funcCNPs and PM-CNPs, indicates the formation of nanopartitional groups in the phenolic and alcoholic compounds.”
Pterocarpus marsupium Roxb. heartwood extract synthesized chitosan nanoparticles and its biomedical applications DOI: 10.1186/s43141-020-00033-x -
Water (H2O) confidence 1.0
“A peak at 1629 The thermal stability of Fe(OH) was analyzed by ing vibration of water molecules attached to the 2 TGA under an air atmosphere at a heating rate of”
Synthesis and characterizations of nanosized iron(II) hydroxide and iron(II) hydroxide/poly(vinyl alcohol) nanocomposite DOI: 10.1002/app.32296 -
C c single bond confidence 1.0
“The band 818 cm-1 is assigned with the C-C 1629 cm-1 is associated with the Carbonyl (C=C) stretching of alkanes.”
Veeramani 等 - 2022 - Vitamin Aand C-rich Pouteria camito fruit derive DOI: 10.4314/ahs.v22i1.78
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