What absorbs at 990 cm⁻¹ in an FTIR spectrum?
A band near 990 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 990 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) | 7 | 7 | 1.0 |
| Methacrylate | 7 | 7 | 1.0 |
| C-O single bond | 7 | 7 | 1.0 |
| Acetate | 7 | 7 | 1.0 |
| Carbohydrate | 5 | 5 | 1.0 |
| Alkyl C-H | 3 | 3 | 1.0 |
| Metal oxygen | 3 | 3 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| Silicon (Si) | 3 | 2 | 1.0 |
| Alkene (C=C) | 2 | 2 | 1.0 |
| Phosphate (PO4) | 2 | 2 | 1.0 |
| Amide | 2 | 2 | 1.0 |
| C c single bond | 2 | 2 | 1.0 |
| Silicon-oxygen (Si-O) | 2 | 1 | 1.0 |
| Fatty acid | 2 | 1 | 1.0 |
| Phosphorus | 1 | 1 | 1.0 |
| Silicate | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| C n single bond | 1 | 1 | 1.0 |
| Bromine | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Silanol (Si-OH) | 1 | 1 | 1.0 |
| Fluorine (C-F) | 1 | 1 | 1.0 |
| C-S single bond | 1 | 1 | 1.0 |
| N-O bond | 1 | 1 | 1.0 |
| Ring structure | 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 |
|---|---|---|---|
| starch | 990, 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 990 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
-
Fatty acid confidence 1.0
“different trans fatty acid contents and the other is to integrate 966cm(cid:2)1 945cm(cid:2)1 the area under band between 990 and limits.”
Quantification of trans fatty acid content in French fries of local food service retailers using attenuated total reflection ⠍ Fourier transform infrared spectroscopy DOI: 10.1016/j.foodchem.2010.09.078 -
Acetate confidence 1.0
“In the cornstarch, PVP:NH4Br polymer blend about molecular interaction, variation of chemical bonding in C-O electrolytes attain characterization peaks at 990 and polymer blend electrolytes on the addition of salt.”
Jothi 等 - 2021 - Proton conducting polymer electrolyte based on cor DOI: 10.1007/s11581-020-03792-2 -
Acetate confidence 1.0
“Bands occurring at around 990 and 1073 are attrib940cm(cid:2)1 610-715cm(cid:2)1 and are due to C-O-H ring vibration uted to CH 2-O-CH stretching (You et al., 2009;”
Investigations on different starches as depressants for iron ore flotation DOI: 10.1016/j.mineng.2013.05.004 -
C c single bond confidence 1.0
“1480cm-1 are due to quadrant and semithe peaks at 1490 and FTRamanwasduetoCH 3inplanebendingvibrations[22].Theband 990cm-1 circle stretching of C C bonds respectively [16].”
Nagabalalsubramanian 等 - 2009 - A scaled quantum mechanical approach of vibrationa DOI: 10.1016/j.saa.2009.10.002 -
Alkyl C-H confidence 1.0
“1620cm-1 1200cm-1 1650 and and the out-of-plane bending vibrations are for C-CH stretching vibration and is combined with 3 990cm-1.”
Vibrational spectroscopy [FTIR and FTRaman] investigation, computed vibrational frequency analysis and IR intensity and Raman activity peak resemblance analysis on 4-chloro 2-methylaniline using HF and DFT [LSDA, B3LYP and B3PW91] calculations DOI: 10.1016/j.saa.2010.12.068 -
Acetate confidence 1.0
“Starting with cm-1 low wave numbers, the band at 990 is due to the C-O-C stretch vibration and OH groups.”
Rouhani 等 - 2016 - Purification and functionalization of nanodiamond DOI: 10.1016/j.msec.2016.02.075 -
Phosphate (PO4) confidence 1.0
“A reduction of the hydroxyl (OH) groups Ti1Zr1P9 content intensifies and defines a peak at 990 cm-1 P-O-R (-OH occurred as the FTIR broad peak at 3350 which is directly related to the contribution of stretching) stretching vibrations.”
Sunarso 等 - 2008 - Characterization of hybrid organic and inorganic f DOI: 10.1016/j.ssi.2008.02.066 -
N-O bond confidence 1.0
“In contrast, the spectra of linseed oil cm-1 cm-1 (Figure 11) initially showed no peaks at 990 or 960”
Wang 等 - 2008 - Fourier transform infrared spectra of drying oils DOI: 10.1021/jf073545m
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