What absorbs at 1699 cm⁻¹ in an FTIR spectrum?
A band near 1699 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 1699 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) | 7 | 7 | 1.0 |
| Carbonyl (C=O) | 6 | 6 | 1.0 |
| Ester | 5 | 5 | 1.0 |
| Alkyl C-H | 4 | 4 | 1.0 |
| Methacrylate | 4 | 4 | 1.0 |
| Ketone | 4 | 4 | 1.0 |
| Amide | 4 | 4 | 1.0 |
| Acetate | 4 | 4 | 1.0 |
| Alkene (C=C) | 2 | 2 | 1.0 |
| Metal oxygen | 2 | 2 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| N h | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.
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 1699 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
-
Metal oxygen confidence 1.0
“A small band at the correspond to (1 0 1), (0 0 4), (2 0 0), (1 0 5), (2 1 1), (2 0 4), (1 1 6), cm-1 cm-1 and 1107 corresponds to Ti O C stretching mode 1699 2 0) and (2 1 5) plane values.”
Synthesis and characterization of polypyrrole/TiO2 composites by chemical oxidative method DOI: 10.1016/j.ijleo.2012.02.029 -
Hydrogen bond confidence 1.0
“Moreover, the peaks at 1699 and 2KBrpellets.TheinteractionofwaterwithKBrmightshiftthepeak increasing temperature might be due to that the hydrogen bonds 3500cm-1”
Hsu 和 Lin - 2009 - Rapid examination of the kinetic process of intram DOI: 10.1016/j.tca.2008.12.008 -
Carboxyl (COOH) confidence 1.0
“2-HP-(cid:2)-CD-TEL × 19 July 2013 Received lenges, we have synthesized a complex with stability constant (Kc) of 2.39 The in revised form 5 September 2013 Received cm-1 2-HP-(cid:2)-CD-TEL absence in the FTIR spectrum of complex of the cha”
Telmisartan complex augments solubility, dissolution and drug delivery in prostate cancer cells DOI: 10.1016/j.carbpol.2013.09.077 -
Carbonyl (C=O) confidence 1.0
“(%) narrow peak at 1699.29 is due to the carbonyl group of ester (eV) untreated RTV POPT-RTV (C=O linkage (ester group), whereas the carbonyl group carbonyl”
Novel pulsed oxygen plasma mediated surface hydrophılizatıon of ritonavır for the enhancement of wettability and solubility DOI: 10.1016/j.jddst.2021.102497 -
Ester confidence 1.0
“In the amide I region, a large negative peak around Q peak with weak negative side peaks (Figure 3), suggests that CdO cm-1, appeared at 1674 and the peaks at 1699, 1685, 1664, the effect of Q A/Q reduction on the 10a-ester vibration B cm-1”
Suzuki 等 - 2005 - Fourier transform infrared spectrum of the seconda DOI: 10.1021/bi051237g -
Carboxyl (COOH) confidence 1.0
“LLM confirmed rule peak-group candidate”
Wang 等 - 2012 - Controlled network structure and its correlations DOI: 10.1039/c2ra00021k -
Acetate confidence 1.0
“In addition, a C=O peak observed at 1699 cm-1 cm-1, systems were at 2852 and 2939 corresponding to C-H symmetric and asymcm-1, in addition to a peak at 1413 cm-1, corresponded to the CH2 detected in all samples.”
Structural Conformation Comparison of Different Clear Aligner Systems: An In Vitro Study DOI: 10.3390/dj10050073 -
Acetate confidence 1.0
“behavior reflects the highly crystalline structure foregoing is a typical broadening and shift of the of menthol or more precisely the absence of cm-1 C=O band at 1699 of capric acid to a higher amorphous regions which usually undergo glass”
Ali 等 - 2020 - New insight into single phase formation of capric DOI: 10.4314/tjpr.v19i2.19
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