What absorbs at 1745 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1745 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 fixed 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 1745 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

• Hydroxyl (O-H) confidence 1.0

  “In the structure of untreated MOS, major bands at 3291 -OH and -NH groups, 2922-OH stretching, 1745-carboxyl and carbonyl groups of 2”

  Adsorption Kinetic and Isotherms of Reactive Red 120 on <i>Moringa oleifera</i> Seed as an Eco-Friendly Process DOI: 10.1016/j.molstruc.2019.05.106
• Aldehyde (CHO) confidence 1.0

  “cm(cid:3)1 1747cm(cid:3)1 1745cm(cid:3)1 peak at 1745 on both spectra exhibited similar intensity for which showed stronger than that at of C4 cm(cid:3)1 the content of aldehydes, ketones and carbonyl stretching vibrain intensity.”

  Chen 等 - 2014 - Determination of chemical changes in Isatis indigo DOI: 10.1016/j.saa.2014.01.048
• Ester confidence 1.0

  “[47], who obtained a sharp peak at 1745 associated with the stretching-shaking of ester carbonyl functional sets of triglycerides.”

  Characterizing the Bioactive Ingredients in Sesame Oil Affected by Multiple Roasting Methods DOI: 10.3390/foods11152261
• Alkyl C-H confidence 1.0

  “3), it is clear that the cm-1), cm-1 valence vibrations of acetyl C =O groups (1745 alihighest value comes at 1732 intensity (associated cm-1), phatic C-H deformation vibrations in CH (1374 to acetyl C =O groups), which registers a coeffici”

  Acetylation of tropical hardwood species from forest plantations in Costa Rica: an FTIR spectroscopic analysis DOI: 10.1186/s10086-020-01898-9
• Alkyl C-H confidence 1.0

  “It was observed that ruminant cm(cid:0) 0.875 0.978 0.074 0.938 1.000 0.031 1.000 0.957 0.021 0.944 0.957 0.050 1 2900-2800 fat samples were positively correlated to the bands Beef cm(cid:0) cm(cid:0) (C-- 1 1 (C-H symmetric stretching), 17”

  Comparison and chemical structure-related basis of species discrimination of animal fats by Raman spectroscopy using near-infrared and visible excitation lasers DOI: 10.1016/j.lwt.2020.110105
• Amide confidence 1.0

  “The frequency values of this band was higher for example, the ratios of dipicolinic acid band or the marker band 1279cm(cid:2)1 1545cm(cid:2)1 and (Amide II band) (Helm & Naumann, (1744.94±1.55) for Micrococcus species compared to Bacillus”

  Use of Fourier transform infrared spectroscopy for rapid comparative analysis of Bacillus and Micrococcus isolates DOI: 10.1016/j.foodchem.2008.08.063
• Ester confidence 1.0

  “the absorption cm(cid:1)1 acylglycerolsandFAMEduringbiodieselproduction.10Satyarthi peak around 1745 is due to presence of an ester carbonyl group.4 et al.”

  Evaluation of the performance and emission and spectroscopic analysis of an improved soy methyl ester DOI: 10.1039/c9ra04342j
• Acetate confidence 1.0

  “The FTIR analysis showed the 3297-3355 -OH - cm-1 presence of a peak at due to the stretching vibration mode of and cm-1 NH groups, and a peak at 1745 due to the C=O stretching in carboxylic group.”

  Removal of Hexavalent Chromium by Cross-Linking Chitosan and N,N’-Methylene Bis-Acrylamide DOI: 10.1007/s40710-020-00447-2