What absorbs at 1686 cm⁻¹ in an FTIR spectrum?
A band near 1686 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 1686 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 | 9 | 7 | 1.0 |
| Carbonyl (C=O) | 7 | 6 | 1.0 |
| Carboxyl (COOH) | 5 | 4 | 1.0 |
| Methacrylate | 4 | 4 | 1.0 |
| Acetate | 4 | 4 | 1.0 |
| Alkene (C=C) | 3 | 3 | 1.0 |
| Ketone | 3 | 3 | 1.0 |
| Ester | 3 | 3 | 1.0 |
| N h | 2 | 2 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| Alkyl C-H | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Urea | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Protein beta sheet | 1 | 1 | 1.0 |
| Protein beta turn | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Methoxy (OCH3) | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| Protein | 1 | 0 | 1.0 |
| Nitro (NO2) | 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 |
|---|---|---|---|
| TiO2 | 1686, 1700, 1093 | Methacrylate, Carboxyl (COOH) | 1 |
| polyurethane | 1686, 2270, 1700 | Methacrylate, Carbonyl (C=O), Amide | 1 |
| copper oxide | 1686, 624, 1384 | Methacrylate, Carbonyl (C=O), Amide | 1 |
| TiO | 1686, 1730, 1699 | Methacrylate, Carboxyl (COOH) | 1 |
| AgNPs | 1686, 1232, 1048 | Methacrylate, Amide | 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 1686 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
-
Aromatic ring confidence 1.0
“cm-1 Bands at 1686 and 1528 were attributed to aromatic C═C groups.”
Salem 等 - 2019 - Synthesis of compounds having antimicrobial activi DOI: 10.1016/j.bioorg.2019.03.013 -
confidence 1.0
“(2021) managed to generate maximum PD peaks the 1686 cm-1 peak shows the presence of alkene compounds (C=C), and the 1496 and 968 W/cm2 of 0.180 in their single-chamber MFCs using leachate as the substrate [58].”
Impact of Dragon Fruit Waste in Microbial Fuel Cells to Generate Friendly Electric Energy DOI: 10.3390/su15097316 -
Acetate confidence 1.0
“48 different peaks at 3428 (O-H stretch of phenols), 2918 (N-H bond of ammonium ions), 2853 (O49 50 H stretch of carboxylic acids), 1686 (C=O stretch of α, β unsaturated carboxylic acids), 1606 (N51”
Yugandhar 等 - 2019 - Biofabrication, characterization and evaluation of DOI: 10.1088/2053-1591/ab0db9 -
Acetate confidence 1.0
“As for the band centred at 1686 C=O stretching vibration of undissociated benzoic acid [13] which could be attached to the TiO 2 surface through either unidentate coordination or hydrogen bonding.”
Augugliaro 等 - 2008 - Photocatalytic oxidation of aromatic alcohols to a DOI: 10.1016/j.apcata.2008.07.038 -
Acetate confidence 1.0
“A sharp and deep band due to C=O stretching and observed along with all drug peaks indicating glipñC-O group was observed at 1685.89 cm-1 izide stability in cocrystals.”
Batool 等 - 2019 - USE OF GLUTARIC ACID TO IMPROVE THE SOLUBILITY AND DOI: 10.32383/appdr/94246 -
Alkyl C-H confidence 1.0
“]C�N+]C�C was assigned to the ring and the band at 1686cm-1 C�C was assigned to the aliphatic stretching, ˚ C2-C3�1.329 although it is not possible to discard a contribution of the A).”
Cordeiro 等 - 2019 - A Novel Zn-II Complex Bearing Two Monodentate (4-M DOI: 10.1155/2019/7876495 -
Amide confidence 1.0
“appeared due to hydroxyl group while, band at 2924 was Biogenic AgNPs probe-based colorimetric detection of metal ions C(cid:3)(cid:3)H found to correspond to stretching, while another small peak The at 1743.97 was found associated with str”
Desai 等 - 2020 - Selective and sensitive colorimetric detection of DOI: 10.1016/j.btre.2019.e00404 -
Carbonyl (C=O) confidence 1.0
“To better describe phase-separation in studied samples after storage, we identified the For TPU-382(PCL)-0.3 the second derivatives allow to select the following absorption positions of the bands of the urethane and ester carbonyl groups [3”
The Influence of Long-Time Storage on the Structure and Properties of Multi-Block Thermoplastic Polyurethanes Based on Poly(butylene adipate) Diol and Polycaprolactone Diol DOI: 10.3390/ma16020818
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