What absorbs at 2818 cm⁻¹ in an FTIR spectrum?
A band near 2818 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 3 cited sources
Quick answer
A band near 2818 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 |
|---|---|---|---|
| N h | 2 | 2 | 1.0 |
| Ammonium | 1 | 1 | 1.0 |
| Secondary amine | 1 | 1 | 1.0 |
| Alkyl C-H | 1 | 1 | 1.0 |
Ranking reflects accumulated literature evidence, not a single authoritative 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 2818 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
“1 clearly shows that peaks at 2818, 2850, 2880 and y1 2920 cm are commonly observed for all the films in spite of the different shape of the CH stretching band.”
Tang 等 - 2004 - Study the effect of O-2 addition on hydrogen incor DOI: 10.1016/j.diamond.2003.10.032 -
N h confidence 1.0
“ν active mode occurs at Price et al., 1991) and lent to the calculated An alternative 2 NH+ 2818cm-1 4 ν the band at is ascribed to an overtone of the NH+”
Abdel-Hak 等 - 2020 - In situ micro-FTIR spectroscopic investigations of DOI: 10.5194/ejm-32-469-2020 -
confidence 1.0
“In the IR cm1, absorption spectrum of the UA crystals, we observed the C-N stretching at ~ 1066 the C = C cm1, cm1, stretching peak at ~ 1577 the C = O stretching peak at ~ 1641 the vibration stretching peaks cm1, cm1 of the O-H stretching”
Lin 等 - 2022 - Observation and identification of autofluorescent DOI: 10.21203/rs.3.rs-1476780/v1
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 confidence-rated evidence chain — in seconds.