What absorbs at 1378 cm⁻¹ in an FTIR spectrum?
A band near 1378 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 1378 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 |
|---|---|---|---|
| Alkyl C-H | 20 | 18 | 1.0 |
| Methacrylate | 8 | 7 | 1.0 |
| Acetate | 8 | 7 | 1.0 |
| C-O single bond | 6 | 6 | 1.0 |
| Methoxy (OCH3) | 6 | 5 | 1.0 |
| Amide | 6 | 5 | 1.0 |
| Carboxyl (COOH) | 5 | 5 | 1.0 |
| Hydroxyl (O-H) | 4 | 4 | 1.0 |
| Carbonyl (C=O) | 4 | 4 | 1.0 |
| Ketone | 3 | 3 | 1.0 |
| Ester | 3 | 3 | 1.0 |
| Secondary amine | 3 | 2 | 1.0 |
| C n single bond | 3 | 2 | 1.0 |
| Aromatic ring | 2 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Nitrate | 1 | 1 | 1.0 |
| Boron nitrogen | 1 | 1 | 1.0 |
| Methyl | 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 |
|---|---|---|---|
| silica | 1378, 1100, 1080 | Alkyl C-H, Methacrylate, Acetate | 1 |
| PVC | 1378, 834, 1195 | Alkyl C-H, Methacrylate, Acetate | 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 1378 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
-
Alkyl C-H confidence 1.0
“At low wavenumber, the peak at cm-1 cm-1 1450 corresponds to both CH3 and CH2 bending vibration and at 1378 for C-H bending vibration.”
Dahham 等 - 2018 - The Influences of Zirconium Dioxide on ENR-25ZrO2 DOI: 10.1088/1742-6596/1019/1/012055 -
Acetate confidence 1.0
“[25], in the region of 11001000 cm-1 peak for C-O symmetric stretching for epoxy group and at 1378 and 1448 shows C-H bending in rubber.”
Ismail 等 - 2015 - Effect of Radiation on Properties of ENRPVCSiO2 DOI: 10.1063/1.4931308 -
Boron nitrogen confidence 1.0
“The band at 800 can be sp2 assigned to out-of-plane bending of the B-N-B bonds, cm-1 whereas the band at 1378 can be related to in-plane sp2 stretching of B-N bonds [28].”
Kim 等 - 2015 - One-Pot Synthesis of h-BN Fullerenes Usinsg a Grap DOI: 10.1007/s12540-015-5043-0 -
Alkyl C-H confidence 1.0
“LLM confirmed rule peak-group candidate”
Kumar 和 Rao - 2018 - Structural and electrochemical properties of PVP-C DOI: 10.1088/2053-1591/aace40 -
Hydroxyl (O-H) confidence 1.0
“The The band, band, ''25-27 ''25-27 The The band band at at at at about about 1454 1454 CH3 CH3 deformation, deformation, and and -CCXY1 -CCXY1 symmetric symmetric stretching stretching vibration vibration is is due due to to -Cl-i2, -Cl-i2”
Liu 等 - 2006 - Characterization of the basidiomycetes Thelephora DOI: 10.1117/12.710905 -
Alkyl C-H confidence 1.0
“is correlated with -OH bending, C-O-H bending, and C-H The band at about The band at about 1378 cm-1”
Liu 等 - 2006 - A study of the mushrooms of boletes by Fourier tra DOI: 10.1117/12.667136 -
Nitrate confidence 1.0
“3411.84 3446 H-O-H bending vibration 1617.15 1617.36 1627.63 1634 Nitrate group stretching 1378.13 1384.4 1384.47 1385”
Investigation on structural, optical and electrical nature of pure and Cr-incorporated cobalt oxide nanoparticles prepared via co-precipitation method for photocatalytic activity of methylene blue dye DOI: 10.1007/s10854-020-04708-6 -
Hydroxyl (O-H) confidence 1.0
“The IR peaks at 1378 and 1375 TME and TAE were attributed to the OH stretching vibrations of phenolic groups and C-H deformations of aliphatic groups, respectively (Chupin et al.”
Abdulmajid 等 - 2019 - Physicochemical Studies of Tamarind Shell Tannins DOI: 10.1039/C4RA10691A
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