What absorbs at 1663 cm⁻¹ in an FTIR spectrum?
A band near 1663 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 1663 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 | 22 | 21 | 1.0 |
| Carboxyl (COOH) | 11 | 11 | 1.0 |
| Carbonyl (C=O) | 11 | 10 | 1.0 |
| Methacrylate | 10 | 10 | 1.0 |
| Acetate | 10 | 10 | 1.0 |
| Ketone | 9 | 9 | 1.0 |
| Ester | 9 | 9 | 1.0 |
| Hydroxyl (O-H) | 4 | 4 | 1.0 |
| N h | 3 | 3 | 1.0 |
| Alkyl C-H | 3 | 3 | 1.0 |
| Secondary amine | 2 | 2 | 1.0 |
| C c single bond | 2 | 2 | 1.0 |
| Methoxy (OCH3) | 2 | 2 | 1.0 |
| Alkene (C=C) | 2 | 2 | 1.0 |
| Protein random coil | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Urea | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| C-O single bond | 1 | 1 | 1.0 |
| C=n | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Aldehyde (CHO) | 1 | 1 | 1.0 |
| Amine primary | 1 | 1 | 1.0 |
| Urethane | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Protein beta turn | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Chlorine | 1 | 1 | 0.7 |
| Protein alpha helix | 1 | 1 | 0.3 |
| Ring structure | 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 |
|---|---|---|---|
| polyamide | 1663, 1541, 1609 | Amide, Carbonyl (C=O), Methacrylate | 2 |
| polyurethane | 1663, 2270, 1700 | Methacrylate, Carbonyl (C=O), 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 1663 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
-
Hydroxyl (O-H) confidence 1.0
“S1 S1-12h S1-24h S1-48h S1-72h S1-1 week Remarks 461.1 461.1 461.1 450.9 471.3 420.4, 416.1 Peak intensity changes as hydration time increases 522.2 522.2 527.3 527.3 522.2 532.4 Peak intensity changes as hydration time increases SO42(cid:2”
Theoretical and experimental study of structures and properties of cement paste The nanostructural aspects of C–S–H DOI: 10.1016/j.jpcs.2011.05.001 -
Protein beta turn confidence 1.0
“Peaks at 1663 and 1665 were mostly assigned to β-turn formation [20,29].”
Fevzioglu 等 - 2020 - Quantitative approach to study secondary structure DOI: 10.1016/j.ijbiomac.2020.07.299 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
Juarez-de la Rosa 等 - 2012 - Effects of thermal treatments on the structure of DOI: 10.1007/s10853-011-5878-9 -
Amide confidence 1.0
“FTIR spectra showed the amide I band Key words: stretching peak at 1663 of polyamide membranes polyamides;”
Change of chemical composition and hydrogen bonding behavior due to chlorination of crosslinked polyamide membranes DOI: 10.1002/app.25657 -
Alkene (C=C) confidence 1.0
“cm-1 The characteristics of the acrylate group were determined by the absorption band of 1663 and 815 (-CH=CH 2=CH-COO-) which related to the acrylate double bond 2) and vinyl functionality of (CH”
Mudri 等 - 2020 - Comparative Study of Aromatic and Cycloaliphatic I DOI: 10.3390/polym12071494 -
Amide confidence 1.0
“FTIR spectral analysis of free nisin (Figure 2B-I) revealed O-H stretch of COOH group cm-1, cm-1 cm-1 appearing at 3286 2927 peak represented the C-H symmetrical stretching, 1663 cm-1 cm-1 attributed to amide group, 1528 was due to bending”
Niaz 等 - 2020 - Alginate-caseinate based pH-responsive nano-coacer DOI: 10.1016/j.ijbiomac.2019.11.177 -
Acetate confidence 1.0
“3 cm-1), cm-1), stretching vibration of CH (2872.99 amide I or C=O stretching (1662.82 amide II or 3 cm-1), N-H bending and stretching (1540.04 C=C bending in aromatic rings of phenolic compounds”
Encapsulation of olive leaf phenolics within electrosprayed whey protein nanoparticles; production and characterization DOI: 10.1016/j.foodhyd.2019.105572 -
confidence 1.0
“In-phase out-of-plane hydrogen deformation of ~ 830 para-substituted phenyl groups [22] cm-1 Amide I band (C=O stretching - dominant contributor, 1663 Peaks for fully aromatic C-N stretching, and C-C-N deformation vibration polyamide in a s”
Tang 等 - 2009 - Effect of membrane chemistry and coating layer on DOI: 10.1016/j.desal.2008.04
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