What absorbs at 1625 cm⁻¹ in an FTIR spectrum?
A band near 1625 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 1625 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 |
|---|---|---|---|
| Protein beta sheet | 17 | 16 | 1.0 |
| N h | 17 | 16 | 1.0 |
| Hydroxyl (O-H) | 16 | 16 | 1.0 |
| Amide | 15 | 15 | 1.0 |
| Alkene (C=C) | 13 | 13 | 1.0 |
| Carboxyl (COOH) | 12 | 12 | 1.0 |
| Water (H2O) | 12 | 11 | 1.0 |
| Carbonyl (C=O) | 11 | 11 | 1.0 |
| Methacrylate | 7 | 7 | 1.0 |
| Ketone | 7 | 7 | 1.0 |
| Ester | 7 | 7 | 1.0 |
| Acetate | 7 | 7 | 1.0 |
| Secondary amine | 6 | 6 | 1.0 |
| Aromatic ring | 6 | 6 | 1.0 |
| Alkyl C-H | 4 | 4 | 1.0 |
| Ring structure | 4 | 4 | 1.0 |
| Protein | 3 | 3 | 1.0 |
| Ammonium | 2 | 2 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| Protein random coil | 2 | 2 | 1.0 |
| C=n | 2 | 1 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| Protein alpha helix | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Amino acid | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Quinone | 1 | 1 | 1.0 |
| Nitrogen heterocycle | 1 | 1 | 1.0 |
| Aldehyde (CHO) | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Silanol (Si-OH) | 1 | 1 | 1.0 |
| Lignin | 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 |
|---|---|---|---|
| graphene oxide | 1625, 1150, 3400 | Hydroxyl (O-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 1625 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
-
Hydroxyl (O-H) confidence 1.0
“The peak at 1625 in BC was due to OH Quetiapine fumarate at different pH's.”
Arikibe 等 - 2019 - pH-Responsive Studies of Bacterial CelluloseChito DOI: 10.1002/slct.201902290 -
Carboxyl (COOH) confidence 1.0
“absorption band that appeared at 1625 is due to the asymmetric stretching vibration of 3.3.9 FTIR Spectroscopy carboxylate group.”
Bamigbola 等 - 2018 - Isolation and Characterization of Cola acuminata G DOI: 10.9734/JPRI/2018/14526 -
Alkene (C=C) confidence 1.0
“The peak at 1625 cm-1 corresponds to a C=C bond in an aromatic ring and the peak at 1060 cm-1”
Daud 等 - 2017 - Functionalizing Graphene Oxide with Alkylamine by DOI: 10.3390/nano7060135 -
Hydroxyl (O-H) confidence 1.0
“The bands observed at 1625 2 cm(cid:1)1 cm(cid:1)1 strong F 1468 and 1385 may be either due to the OH group vibration mode, two weak modes appeared in the 2g”
Structural and spectroscopic studies of rare earths doped ceria (RELa,Sc,Yb_CeO2) nanopowders DOI: 10.1016/j.ceramint.2014.01.076 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
Lehmkuhl 等 - 2015 - Fabrication of IR-transparent microfluidic devices DOI: 10.1039/C5LC00759C. -
Aromatic ring confidence 1.0
“The peak at 3 2 P P cm-1 1625 is assigned to the aromatic ring C=C.”
Experimental study on the influence of water immersion on spontaneous combustion of anthracite with high concentrations of sulfur-bearing minerals DOI: 10.1007/s10973-019-09073-z -
Amide confidence 1.0
“The protein's secpeaks at 1652 and 1547 corresponded to the cm(cid:1)1 (cid:2)-helix/random ondary structure and the composition of each component in coil structure, the peak at 1625 amide I and II bands of these ir spectra were estimated (”
Pressure dependence of human fibrinogen correlated to the conformational [alpha]-helix to [beta]-sheet transition: An Fourier transform infrared study microspectroscopic study DOI: 10.1002/bip.20012 -
Carboxyl (COOH) confidence 1.0
“The carboxylate peak at 1625 is weak and does not interfere”
Loginova 等 - 2016 - Quantification of copolymer composition (methyl ac DOI: 10.1039/C5AY02264A.
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.