What absorbs at 1775 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1775 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

Ranking reflects accumulated literature evidence, not a single authoritative rule. Always confirm against your sample context.

Possible materials

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 1775 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

• Carboxyl (COOH) confidence 1.0

  “Spectrum FTIR Carboxymethyl kappa-carrageenan Based on the FTIR spectrum, it appears that some of the hydroxyl groups have been replaced with carboxyl cm-1 cm-1 and 1417 confirming groups, indicated by the appearance of absorption peaks at”

  The capability of nanomagnetite carboxymethyl kappa-carrageenan coated to adsorp metal ions DOI: 10.1063/5.0000680
• Acetate confidence 1.0

  “The absence of the vibration band located around 1775 is attributed to the elongated vibrations of the specific C=O bond of the hemicellulose residues”

  Part A: Biodegradable Bio-Composite Film Reinforced with Cellulose Nanocrystals from Chaetomorpha linum into Thermoplastic Starch Matrices DOI: 10.3390/polym15061542
• Carbohydrate confidence 1.0

  “Sci.2022,12,9645 5of9 and 1775 cm-1 which are attributed to the carbohydrates and O-H stretching vibrations”

  Botanical Origin Assessment of Honey Based on ATR-IR Spectroscopy: A Comparison between the Efficiency of Supervised Statistical Methods and Artificial Intelligence DOI: 10.3390/app12199645
• Hydroxyl (O-H) confidence 1.0

  “cm-1, cm-1, O-H, C=O, C=C, -CH 2, C-O stretching, and C-H bending at 3741.18 1774.84 cm-1, cm-1, cm-1, cm-1, 1689.04 1511.76 1182.03 and 882.79 respectively.”

  Evaluation of Structural and Optical Properties of Graphene Oxide-Polyvinyl Alcohol Thin Film and Its Potential for Pesticide Detection Using an Optical Method DOI: 10.3390/photonics9050300
• Acetate confidence 1.0

  “1153cm(cid:3)1 which the carbonyl stretching vibration of six-membered cyclic (C-O stretching of ester) and (C-N stretching of aliphatic ester).17,18 1760cm(cid:3)1, anhydrides exhibited unique peaks at 1800 and amine and/or C-O stretching”

  DSC-FTIR microspectroscopy used to investigate the heat-induced intramolecular cyclic anhydride formation between Eudragit E and PVA copolymer DOI: 10.1038/pj.2011.15;
• Acetate confidence 1.0

  “The absorption bands observed at 1775 cm-1 and 1716 were attributed to the asymmetric and symmetric stretching of C=O in the imide ring, Polymers2017,9,734”

  Preparation and Evaluation of a Polyimide-Coated Ultrafine Gilt Molybdenum Wire and Its Knitted Mesh Used for Electromagnetic Reflectors DOI: 10.3390/polym9120734
• Alkyl C-H confidence 1.0

  “In the Figure 4 (A) the shows crystalline and 2850 (CH stretching), 1775 (C=O stretchIndian Journal of Pharmaceutical Education and Research | Vol 52 | Issue 4 [Suppl] | Oct-Dec, 2018”

  Udapurkar 等 - 2018 - Diosmin Phytosomes Development, Optimization and DOI: 10.5530/ijper.52.4s.73
• confidence 0.8

  “Attributed to specific vibration of thiophene.”

  Surface Characterization of Modified Electrodes Based on 4-(Azulen-1-yl)-2,6-bis((E)-2-(thiophen-2-yl)vinyl)pyridine DOI: 10.3390/sym14122506