What absorbs at 1698 cm⁻¹ in an FTIR spectrum?
A band near 1698 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 1698 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 |
|---|---|---|---|
| Carboxyl (COOH) | 8 | 8 | 1.0 |
| Carbonyl (C=O) | 7 | 7 | 1.0 |
| Amide | 5 | 5 | 1.0 |
| Alkyl C-H | 3 | 3 | 1.0 |
| N h | 3 | 3 | 1.0 |
| Alkene (C=C) | 3 | 3 | 1.0 |
| Methacrylate | 3 | 3 | 1.0 |
| Ketone | 3 | 3 | 1.0 |
| Ester | 3 | 3 | 1.0 |
| Acetate | 3 | 3 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| Urethane | 2 | 2 | 1.0 |
| Aldehyde (CHO) | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| Fatty acid | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 0.9 |
| Protein beta sheet | 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 |
|---|---|---|---|
| PVA | 1698, 1660, 2930 | Alkyl C-H, Carbonyl (C=O), Amide | 1 |
| polyurethane | 1698, 2270, 1700 | Alkyl C-H, Carbonyl (C=O), Amide | 1 |
| Polyurethanes | 1698, 1740, 1728 | Amide, Carbonyl (C=O), Alkyl C-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 1698 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
-
Urethane confidence 1.0
“The peaks at 1698cm-1 and correspond to the urethane carbonyl, and hydrogen”
Two-component waterborne polyurethane_ Curing process study using dynamic in situ IR spectroscopy DOI: 10.1016/j.polymertesting.2018.05.021 -
Acetate confidence 1.0
“The 4 cm-1 synchronous correlation spectrum developed an auto-peak at 1698 and the band 5 cm-1 at 1698 was assigned to the -(C=O)-NHgroup including the ordered hydrogen 6 bonding moieties through both the C=O and N-H groups [18].”
A study of molecular architectural dynamics of crosslinked urethane during photo-aging by two-dimensional infrared correlation spectroscopy DOI: 10.1016/j.polymdegradstab.2020.109242 -
Hydrogen bond confidence 1.0
“The absorption peak at cm-1 cm-1 1698 shifted toward 1725 with the increase of the reaction time, which indicates the reduction of the hydrogen bond with the increase of the reaction time.”
Kim 等 - 2014 - Temperature dependent surface modification of sili DOI: 10.1117/12.2061456 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Surface Modification of Castor OilBased Polyurethane by Polyacrylic Acid Graft using a TwoStep Plasma Treatment for Biomedical Applications DOI: 10.1002/adv.21411 -
Carboxyl (COOH) confidence 1.0
“at 1725 and 1708 and troughs at 1715 and 1698 cm-1 The 1725/1715 features likely arise from a shift of a cm-1 peak could second carboxylic acid, whereas the 1708 arise from a further carboxylic acid or heme propionic acid.”
Rich 和 Breton - 2001 - FTIR studies of the CO and cyanide adducts of full DOI: 10.1021/bi0027332 -
Alkene (C=C) confidence 1.0
“In SEM images obtained, it can be cm-1 Stretching C=O group 1698 observed that particles had quite an irregular shape due to cm-1 Stretching vibrations C=C 1545 aggregation, which could also lead to differences in particle size.”
Influence of Polyvinyl Alcohol (PVA) on PVA-Poly-N-hydroxyethyl-aspartamide (PVA-PHEA) Microcrystalline Solid Dispersion Films DOI: 10.1208/s12249-020-01811-z -
Carbonyl (C=O) confidence 1.0
“for cyclohexanone physisorption on low and intermediate hycm(cid:1)1, which gives a drationlevels are centered at 1690 and 1679 good correlation to experimentally observed peaks (1694 and The calculated spectra of cyclohexanone physisorptio”
Almeida 等 - 2011 - Combined ATR-FTIR and DFT Study of Cyclohexanone A DOI: 10.1021/jp1122129 -
Hydroxyl (O-H) confidence 1.0
“The resting (control) macrophages cm-1 The number of bacteria recovered from demonstrated FTIR spectra at 3412 (O-H cm-1 the host-pathogen interface assay (Table 1) stretch), 1698 (C=O acidic stretch), 1566 cm-1 demonstrated significantly (”
El Mohtadi 等 - 2020 - DIFFERENTIAL ENGULFMENT OF STAPHYLOCOCCUS AUREUS A DOI: 10.17179/excli2020-2766
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