What absorbs at 1705 cm⁻¹ in an FTIR spectrum?
A band near 1705 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 1705 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) | 30 | 25 | 1.0 |
| Carboxyl (COOH) | 19 | 17 | 1.0 |
| Methacrylate | 12 | 12 | 1.0 |
| Ester | 12 | 12 | 1.0 |
| Acetate | 12 | 12 | 1.0 |
| Ketone | 11 | 11 | 1.0 |
| Amide | 11 | 11 | 1.0 |
| Alkyl C-H | 5 | 5 | 1.0 |
| Alkene (C=C) | 4 | 4 | 1.0 |
| Methoxy (OCH3) | 3 | 3 | 1.0 |
| C-O single bond | 3 | 3 | 1.0 |
| Aldehyde (CHO) | 2 | 2 | 1.0 |
| Lignin | 2 | 2 | 1.0 |
| Aromatic ring | 2 | 2 | 1.0 |
| Carbohydrate | 2 | 2 | 1.0 |
| Imide | 1 | 1 | 1.0 |
| Chitosan | 1 | 1 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Hydroxyl (O-H) | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Oxygen heterocycle | 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 | 1705, 1700, 1093 | Methacrylate, Carboxyl (COOH) | 1 |
| polypyrrole | 1705, 1700, 400 | Methacrylate, Carbonyl (C=O) | 1 |
| TiO | 1705, 1730, 1699 | 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 1705 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
-
Acetate confidence 1.0
“(C-H were observed at 2840 stretch) (Figure 6a), 2340, 1705 cm-1 (CdO (C-O At 300 K, the sXPS spectra suggest that there is one binding (both stretch), 1584 stretch), 1387, and 1364 COO-”
Durand 等 - 2010 - Reaction of Formic Acid over Amorphous Manganese O DOI: 10.1021/jp104629j -
Ring structure confidence 1.0
“ring),1547cm-1 stretching,1709cm-1,1706cm-1,1705cm-1 for (b), (c) due to C=C bond for (a),(b),(c) pyrrole 3161cm-1 (a),3399cm-1 3127cm-1for (b),3362cm-1 3128cm-1 respectively due to C=N stretching, for and and for (c) are assigned to the pr”
Synthesis, characterization, morphological and electrical studies of polypyrrole nanostructures DOI: 10.1063/1.5093829 -
Carbonyl (C=O) confidence 1.0
“DSC data of the optimum sample showed almost similar decomposition of carbonyl peak of MA modifier at 1705,07 (461oC), (465oC), when compared to that without asphalt whereas SEM micrograph of the sample showed homogenous temperature distrib”
Preparation and characterisations of maleic anhydride-modified-(asphalt, natural rubber, and polystyrene) blends containing sand aggregate DOI: 10.1063/5.0015735 -
Carbonyl (C=O) confidence 1.0
“1658.5 could be used for the quantitative determinathe carbonyl bands at 1704.8 and 1658.5 cm-1 tion of caffeine in tea extracts.”
Ohnsmann 等 - 2002 - Determination of caffeine in tea samples by Fourie DOI: 10.1007/s00216-002-1503-8 -
Carboxyl (COOH) confidence 1.0
“mercaptoundecanoic acid/Au given in Table II indicm(cid:1)1 3(b)] and of O1s core level at 532.0 eV and 533.3 eV cate that the band frequencies at 1705 and 1400 cm(cid:1)1 OACOO examined by XPS, could be assigned to the were assigned to res”
Proteomic profiling of platelet proteins by trypsin immobilized self-assembled monolayers digestion chip and protein identification using electrospray ionization tandem mass spectrometry DOI: 10.1002/jbm.a.30129 -
Alkene (C=C) confidence 1.0
“2), the strong bands at 1629.24 and cm-1 1705.05 correspond to the absorptions of the double bond (C=C) and carbonyl bond cm-1 981.82 and 930.72 respectively.”
Electrochemical Sensor Based on Thioether Oligomer Poly(N-vinylpyrrolidone)-modified Gold Electrode for Bisphenol A Detection DOI: 10.1002/elan.201900060 -
Acetate confidence 1.0
“to the C=O stretching of an aldehyde group for the band centred at 1705 Moreover, the”
Augugliaro 等 - 2008 - Photocatalytic oxidation of aromatic alcohols to a DOI: 10.1016/j.apcata.2008.07.038 -
Alkyl C-H confidence 1.0
“cm-1 intense peak at 1705 was also found, corresponding to the stretching vibrations of the originating from the aliphatic CH groups in the wavenumber range of 3000-2850 cm-1 2 cm-1, C=O groups [49].”
Determination of the Ni(II) Ions Sorption Mechanism on Dowex PSR2 and Dowex PSR3 Ion Exchangers Based on Spectroscopic Studies DOI: 10.3390/ma16020644
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