What absorbs at 1649 cm⁻¹ in an FTIR spectrum?
A band near 1649 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 1649 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 | 28 | 1.0 |
| Carbonyl (C=O) | 14 | 13 | 1.0 |
| Methacrylate | 11 | 11 | 1.0 |
| Acetate | 11 | 11 | 1.0 |
| Carboxyl (COOH) | 11 | 11 | 1.0 |
| Alkyl C-H | 10 | 10 | 1.0 |
| Ester | 9 | 9 | 1.0 |
| Ketone | 8 | 8 | 1.0 |
| Water (H2O) | 7 | 7 | 1.0 |
| N h | 6 | 5 | 1.0 |
| Hydroxyl (O-H) | 5 | 5 | 1.0 |
| Protein alpha helix | 5 | 5 | 1.0 |
| Secondary amine | 4 | 4 | 1.0 |
| Protein | 4 | 4 | 1.0 |
| C n single bond | 3 | 3 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| Silicon-oxygen (Si-O) | 3 | 2 | 1.0 |
| N-O bond | 2 | 2 | 1.0 |
| Alkene (C=C) | 2 | 2 | 1.0 |
| Siloxane (Si-O-Si) | 2 | 2 | 1.0 |
| Protein beta sheet | 2 | 2 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Phosphorus | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Silanol (Si-OH) | 1 | 1 | 1.0 |
| Amino acid | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| C=n | 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 |
|---|---|---|---|
| cellulose | 1649, 1735, 1650 | Acetate, Methacrylate, Amide | 1 |
| calcium phosphate | 1649, 1070, 1149 | Methacrylate | 1 |
| protein | 1649, 1650, 1640 | Amide, Carbonyl (C=O), Methacrylate | 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 1649 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
“In 41 cm@1 chitosan, the peaks at 1649 and 1579 are attributed to the The BC formed was removed from the fermenting container 42 amino (NH 2) and N@H bending vibrations respectively.”
Arikibe 等 - 2019 - pH-Responsive Studies of Bacterial CelluloseChito DOI: 10.1002/slct.201902290 -
Hydroxyl (O-H) confidence 1.0
“Another band is shown at 1649 cm-1, this band corresponds to a deformation also of OH groups.”
Development of Composite Scaffolds Based on Cerium Doped-Hydroxyapatite and Natural Gums—Biological and Mechanical Properties DOI: 10.3390/ma12152389 -
Protein alpha helix confidence 1.0
“In the average spectrum of the control samples, the line located at 1649 cm-1 associated with an α-helical protein structure [9,21,23,24], and the relative area of its”
A Preliminary Study of FTIR Spectroscopy as a Potential Non-Invasive Screening Tool for Pediatric Precursor B Lymphoblastic Leukemia DOI: 10.3390/molecules -
Water (H2O) confidence 1.0
“In both spectra, the peak at 1649 corresponds to the water adsorbed (Liu et al.”
Daniel 等 - 2020 - Citric acid modified cellulose a cost effective a DOI: 10.1080/15567036.2020.1773963 -
Amide confidence 1.0
“here amide I bands are seen from 1645 to 1649cm-1.Thebandaround1650cm-1, medicine [24], in the diagnosis of mucoviscidosis [25], and hepatoisattributabletoamideI of α-helical lenticular degeneration [26].”
Farhan 等 - 2011 - Comparative study on secondary structural changes DOI: 10.1016/j.cca.2010.11.016 -
Amide confidence 1.0
“To determine the extent of glycation, MS was employed to 1000 cm-1 This determine the mass changes in the protein as a function of Amide I is represented by the peak at 1649 and amide cm-1.”
Mcavan 等 - 2020 - Quantification of protein glycation using vibratio DOI: 10.1039/c9an02318f -
Hydroxyl (O-H) confidence 1.0
“Clearly, the agglomercould be due to the presence of water molecules absorbed by cm-1 samples.[28] ation is observed in all the samples which could be attributed the The observed absorption band at 1649 grains.[30] 2O.[29] to magnetic inter”
Mohammed 等 - 2018 - Enhanced dielectric and optical properties of nano DOI: 10.1088/1674-1056/27/12/128104 -
Protein alpha helix confidence 1.0
“The α-helix bands were centered at 1649 and 1655 cm-1.”
Sadat 和 Joye - 2020 - Peak Fitting Applied to Fourier Transform Infrared DOI: 10.3390/app10175918
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