What absorbs at 2021 cm⁻¹ in an FTIR spectrum?
A band near 2021 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 320,000+ reference spectra and knowledge graph.
Backed by 7 cited sources
Quick answer
A band near 2021 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 |
|---|---|---|---|
| Methacrylate | 10 | 10 | 1.0 |
| Acetate | 10 | 10 | 1.0 |
| Amide | 10 | 10 | 1.0 |
| C-O single bond | 8 | 8 | 1.0 |
| Methoxy (OCH3) | 7 | 7 | 1.0 |
| Alkyl C-H | 7 | 7 | 1.0 |
| Hydroxyl (O-H) | 6 | 6 | 1.0 |
| Carboxyl (COOH) | 5 | 5 | 1.0 |
| Carbonyl (C=O) | 5 | 5 | 1.0 |
| Secondary amine | 4 | 4 | 1.0 |
| C n single bond | 4 | 4 | 1.0 |
| Ketone | 3 | 3 | 1.0 |
| Ester | 3 | 3 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| N h | 2 | 2 | 1.0 |
| Carbon dioxide | 1 | 1 | 1.0 |
| Water (H2O) | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| Nucleic acid | 1 | 1 | 1.0 |
| Amino acid | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| C-S single bond | 1 | 1 | 1.0 |
| Adsorbed carbon monoxide | 1 | 0 | 0.7 |
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 2021 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)
- Reported band
- 2021 cm-1
- Assignment
- Hydroxyl (O-H)
- Material / context
- biodegradable polymer blend electrolytes based on Cornstarch: PVP: NH4Cl; Cornstarch:PVP:NH4Cl polymer blend electrolyte
-
Hydroxyl (O-H)
- Reported band
- 2021 cm-1
- Assignment
- Hydroxyl (O-H)
- Material / context
- absorbent hydrogel polymers
-
C-O single bond
- Reported band
- 2021 cm-1
- Assignment
- C-O single bond
- Material / context
- GB sediment; OU sediment; dental adhesive
-
C-O single bond
- Reported band
- 2021 cm-1
- Assignment
- C-O single bond
- Material / context
- AUS samples; spirit beverage
-
Alkyl C-H
- Reported band
- 2021 cm-1
- Assignment
- Alkyl C-H
- Material / context
- palm oil; geranium essential oil
-
C-S single bond
- Reported band
- 2021 cm-1
- Assignment
- C-S single bond
- Material / context
- —
-
Alkyl C-H
- Reported band
- 2021 cm-1
- Assignment
- Alkyl C-H
- Material / context
- organic matter (OM) in soils
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