What absorbs at 991 cm⁻¹ in an FTIR spectrum?
A band near 991 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 991 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 |
|---|---|---|---|
| Methoxy (OCH3) | 5 | 5 | 1.0 |
| Methacrylate | 5 | 5 | 1.0 |
| C-O single bond | 5 | 5 | 1.0 |
| Acetate | 5 | 5 | 1.0 |
| Alkyl C-H | 3 | 3 | 1.0 |
| C c single bond | 3 | 3 | 1.0 |
| Siloxane (Si-O-Si) | 1 | 1 | 1.0 |
| Silicon-oxygen (Si-O) | 1 | 1 | 1.0 |
| Silicon (Si) | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Nitrogen heterocycle | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Amide | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 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 |
|---|---|---|---|
| chitosan | 991, 1650, 1655 | Acetate, Methacrylate, C-O single bond | 2 |
| starch | 991, 1650, 1540 | Methacrylate, Acetate, C-O single bond | 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 991 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
-
N-O bond confidence 1.0
“80 3250.99,76.51 1687.44,76.79 70 2815.57,32.692423.57,73.51 2069.02,66.041849.56,74.03 3871.87,75.87 2312.85,75.63 1402.29,66.08 753.51,66.68 60 Results And Discussion 3799.54,76.57 2945.45,63.15 673.11,3.44520.46,67.86 1343.49,60.79 1053.”
Gowda 和 Eraiah - 2013 - Synthesis and Structural Studies Of Praseodymium D DOI: 10.1063/1.4791162 -
Alkyl C-H confidence 1.0
“thiophene), 1357.21 (C-N and N-N stretching vibration), 1278.82 (in-plane C-H stretching vibration cm-1, of thiophene), 1145.5 (C-H bending vibration), 991.33, 889.64, and 799.05 wherein the C-H stretching vibration of the thiophene ring wa”
Novel Hemocompatible Imine Compounds as Alternatives for Antimicrobial Therapy in Pharmaceutical Application DOI: 10.3390/pr8111476 -
Acetate confidence 1.0
“It is reported that cm-1, bands are present due to the C-O-C stretching vibration the band at ~ 991 assigned to C-O stretching vibraof polysaccharide in Aloe vera gel but also in starch.”
Novel Starch/Chitosan/Aloe Vera Composites as Promising Biopackaging Materials DOI: 10.1007/s10924-020-01661-7 -
Acetate confidence 1.0
“CC out of plane vibration 991 C-O, C-C 925 COH out of plane vibration 926”
Application of Vibrational Spectroscopic Techniques in the Study of the Natural Polysaccharides and Their Cross-Linking Process DOI: 10.3390/ijms24032630 -
C c single bond confidence 1.0
“The spectra of pentoses (arabinose and xylose) were 210 cm-1, dominated by a band at 991 and 1034 respectively, mainly due to the ν(C-C), 211 ν(C-O) and β(C-CH) vibrations (Edwards, 1976).”
Revisiting the contribution of ATR-FTIR spectroscopy to characterize plant cell wall polysaccharides DOI: 10.1016/j.carbpol.2021.117935 -
Alkyl C-H confidence 1.0
“Thus, the broad band centered at 3327 cm-1 was cm´1 N-H stretching vibration of secondary amines, the peak at 1151 corresponds to C-N vibrations, assigned to N-H stretching vibration of secondary amines, the peak at 1151 cm-1 corresponds to”
Magina 等 - 2016 - High Pressure Laminates with Antimicrobial Propert DOI: 10.3390/ma9020100 -
Acetate confidence 1.0
“Finally, a three bands at 1675, 1670, and 1633 were observed, cm-1 band around 991 is mainly due to C-O stretch which are also related to asparagine, glutamine, and argifrom RNA ribose chain [17, 23].”
Morphological, molecular and FTIR spectroscopic analysis during the differentiation of kidney cells from pluripotent stem cells DOI: 10.1186/s40659-017-0119-6 -
Amide confidence 1.0
“cm-1 cm-1 at 1172 (C-O stretching (Carbohydrates/glycogen, nucleic acids)), 1013 (CO stretching and C-OH bending (DNA and RNA, oligosaccharides, polysaccharides)), cm-1 cm-1 (C-N+-C 991 (C-O stretching (DNA and RNA ribose)) and 914 stretchi”
Fourier-Transform Infrared Spectroscopy as a Discriminatory Tool for Myotonic Dystrophy Type 1 Metabolism: A Pilot Study DOI: 10.3390/ijerph18073800
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