What absorbs at 1338 cm⁻¹ in an FTIR spectrum?
A band near 1338 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 1338 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 | 10 | 10 | 1.0 |
| Amide | 6 | 6 | 1.0 |
| Protein | 5 | 5 | 1.0 |
| Methoxy (OCH3) | 5 | 5 | 1.0 |
| Methacrylate | 5 | 5 | 1.0 |
| Acetate | 5 | 5 | 1.0 |
| N h | 4 | 4 | 1.0 |
| Carboxyl (COOH) | 4 | 4 | 1.0 |
| C-O single bond | 4 | 4 | 1.0 |
| Amino acid | 2 | 2 | 1.0 |
| Borate | 2 | 2 | 1.0 |
| Hydroxyl (O-H) | 2 | 2 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Methyl | 1 | 1 | 1.0 |
| Carbohydrate | 1 | 1 | 1.0 |
| Ammonium | 1 | 1 | 0.8 |
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 |
|---|---|---|---|
| TiO2 | 1338, 1700, 1093 | Alkyl C-H, Methoxy (OCH3) | 1 |
| ZnO | 1338, 1400, 3430 | Alkyl C-H, Methoxy (OCH3), Amide | 1 |
| collagen | 1338, 1408, 1660 | Amide, Alkyl C-H, Methoxy (OCH3) | 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 1338 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
“3A and B, correspondThese bands can be regarded as a fingerprint of the adsorption ingto20and40minofelectrochemicalpolarisation,respectively), of undissociated ethanol, in fact: (i) combined O-H and C-H wagging in ethanol adsorbed via the C”
In situ spectroelectrochemical measurements during the electro-oxidation of ethanol on WC-supported Pt-black, based on sum-frequency generation spectroscopy DOI: 10.1016/j.jpowsour.2010.01.017 -
confidence 1.0
“In the FT-IR spectra of pure and Mn-doped (1%, structure of ZnO NPs and Mn-doped ZnO nanoparticles (Pathak 2.5%,5%,and7%)ZnOnanoparticles,typicalpeakswereobservedat 3442cm-1, 1556cm-1, 1338cm-1, 1080cm-1, 825-665cm-1.”
Khan 等 - 2022 - Microwave-Assisted Green Synthesis of Pure and Mn- DOI: 10.3389/fmats.2021.710155 -
Alkyl C-H confidence 1.0
“Besides, affected TPA's 1435cm-1 1338cm-1 both during conversion to TPA, resulting in and bands are assigned to -CH scissor2”
Nahar 等 - 2022 - A Modified Hydrolysis Method of Decolorizing React DOI: 10.1155/2022/4325506 -
Amide confidence 1.0
“The integrated areas under the amide I and carbohydrate regions as well as the ratio of cm-1 the integrated areas under the region around the 1338 peak and the amide II region were calculated for each”
Imaging of Osteoarthritic Human Articular Cartilage using Fourier Transform Infrared Microspectroscopy Combined with Multivariate and Univariate Analysis DOI: 10.1038/srep30008 -
confidence 1.0
“have a large contribution to the S-state spectra of spinach (Figure 5) are not responsible for the difference in this region, because in the double difference spectra, no specific peaks cm-1 were observed at 1338, 1257, 1228, 1103, and 1097”
Suzuki 等 - 2006 - Structural perturbation of the carboxylate ligands DOI: 10.1021/bi061232z -
Carboxyl (COOH) confidence 1.0
“Aliphatic -CH2 bending 1734 -C O stretch of carboxylic group 1430 -OH in -C plane bending 1594 O stretch of carboxylate anion 1338 1110”
Slightly carbomethylated cotton supported TiO2 nanoparticles as self-cleaning fabrics DOI: 10.1016/j.molcata.2014.11.012 -
Amide confidence 1.0
“Like the amide II and amide III peaks, the cm-1 1338 band confirms the anisotropy of collagen fibrils in cartilage.”
Yin 等 - 2011 - Depth-dependent anisotropy of proteoglycan in arti DOI: 10.1016/j.vibspec.2011.08.005. -
Carbohydrate confidence 1.0
“.Hemicelluloseyielded-CH2,CH,andOHbending 1160cm-1 to cellulose, appears at and the C-O stretch in and-CHwaggingbondcorrespondingtotheloadingsat1453, 1047-1004cm-1 1338cm-1 [35, 36].”
Zhou 等 - 2015 - Multivariate Calibration and Model Integrity for W DOI: 10.1155/2015/429846
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