What absorbs at 1405 cm⁻¹ in an FTIR spectrum?
A band near 1405 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 1405 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 |
|---|---|---|---|
| Carboxyl (COOH) | 8 | 8 | 1.0 |
| Methacrylate | 6 | 6 | 1.0 |
| Acetate | 6 | 6 | 1.0 |
| Alkyl C-H | 5 | 5 | 1.0 |
| Methoxy (OCH3) | 5 | 5 | 1.0 |
| C-O single bond | 5 | 5 | 1.0 |
| Amide | 4 | 4 | 1.0 |
| Hydroxyl (O-H) | 3 | 3 | 1.0 |
| N h | 3 | 3 | 1.0 |
| N-O bond | 2 | 2 | 1.0 |
| Amino acid | 2 | 2 | 1.0 |
| Carbonate | 2 | 2 | 1.0 |
| Ketone | 1 | 1 | 1.0 |
| Ester | 1 | 1 | 1.0 |
| Carbonyl (C=O) | 1 | 1 | 1.0 |
| C c single bond | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Fluorine (C-F) | 1 | 1 | 0.9 |
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 |
|---|---|---|---|
| polypropylene | 1405, 1030, 1600 | Alkyl C-H, Methacrylate, Acetate | 1 |
| ZnO | 1405, 1400, 3430 | Alkyl C-H, Acetate, Methacrylate | 1 |
| PVA | 1405, 1660, 2930 | Alkyl C-H, Acetate, Methacrylate | 1 |
| AgNPs | 1405, 1232, 1048 | 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 1405 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
-
confidence 1.0
“Dobrozhan et al.: Nanocrystalline ZnO films deposited by pulsed spray pyrolysis 1560cm(cid:1)1 can be ascribed to the The bands at 1405 and C-O symmetric and asymmetric stretching vibrations in the”
Dobrozhan 等 - 2015 - Substructural investigations, Raman, and FTIR spec DOI: 10.1002/pssa.201532324 -
Amide confidence 1.0
“4.b, there are two peaks in 1405 and 1614 in Herceptin spectrum that are 6 assigned to amides 1 and 2 similar to all proteins spectra [42].”
Structural, optical and dielectric studies of Ag nanoparticles decorated by herceptin DOI: 10.1016/j.physe.2019.113562 -
Hydroxyl (O-H) confidence 1.0
“FTIR characterization and symmetric carboxylate ion stretch at 1405 It can cm-1 was be observed that the hydroxyl peak of PVA at 3430 Figure 2 shows the FTIR spectra of the raw materials”
Pal 等 - 2006 - Polyvinyl alcohol-glycine composite membranes pre DOI: 10.1088/1748-6041/1/2/001 -
Amide confidence 1.0
“LLM confirmed rule peak-group candidate”
Screening and production of a potential extracellular fungal laccase from Penicillium chrysogenum: Media optimization by response surface methodology (RSM) and central composite rotatable design (CCRD) DOI: 10.1016/j.btre.2019.e00344 -
Alkene (C=C) confidence 1.0
“Four measurements per sample were at 1660-1580, 1445, and 1405 cm-1 can be attributed performed, and using the Smoluchowski equation, to the stretching vibrations of C=C/C=O, N-H and”
Verma 和 Goel - 2023 - Nanofabrication and characterization of green-emit DOI: 10.37819/nanofab.008.299 -
N-O bond confidence 1.0
“At high RH, the 3-NO band is 2-NO band for these two frequency cm-1 split into two wide peaks at 1405 and 1346 components.”
Zhang 等 - 2014 - In Situ Observation on the Dynamic Process of Evap DOI: 10.1021/jp412073c -
Acetate confidence 1.0
“The C-O stretching within the polypropylene cm-3 component of the mask waste was assigned to the peaks at about 1405 [19].”
Physical and Chemical Characteristics of Agricultural-Plastic Wastes for Feasibility of Solid Fuel Briquette Production DOI: 10.3390/su142315751 -
Carbonate confidence 1.0
“LLM confirmed rule peak-group candidate”
The Effect of Low-Processing Temperature on the Physicochemical and Mechanical Properties of Bovine Hydroxyapatite Bone Substitutes DOI: 10.3390/ma15082798
Have a spectrum with this band?
Upload your FTIR spectrum and get a full interpretation report — peak assignments with literature citations, library matches, and a literature-backed analysis — in seconds.