What absorbs at 1738 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1738 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 1738 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

• Carbonyl (C=O) confidence 1.0

  “Appearance of new peak at 1738 corresponding to carbonyl ester stretch indicates possible esterification reaction of carboxylic anion with highly strained epoxy ring leading to ionized epoxide (shown in Fig.”

  Mechanism and Kinetics of Curing of Diglycidyl Ether of Bisphenol A (DGEBA) Resin by Chitosan DOI: 10.1002/pen.24463
• Carboxyl (COOH) confidence 1.0

  “split in three peaks seen at 1738, 1706 and This split indicates that the COOH group is influenced by the absence of the iron center as well as by the symmetry of the porphyrin ring.”

  Doerr 等 - 2008 - Far infrared spectroscopy on hemoproteins A model DOI: 10.1016/j.vibspec.2008.02.003
• Carbonyl (C=O) confidence 1.0

  “From the FTIR spectra, we can see that the stretching vibration of the carbonyl group (C=O) for aliphatic esters is in wave number 1732, 1738, 1737 and 1740 cm-1 for SFA-TMP ester, SFA-Di-TMP ester, SFA-PE ester and SFA-Di-PE ester respecti”

  Jumaah 等 - 2021 - Optimization for esterification of saturated palm DOI: 10.3906/kim-2103-11
• Hydroxyl (O-H) confidence 1.0

  “Full FT-IR experimental study of GU S was reported in Figure 3 in which C=O, C=N, C-O, C-N, N-H and O-H bonds is completely U N clear peaks respectively in 1738, 1607, 1228, 1082, 3816 (broad peak), 2820-3370 (sharp peak) A”

  Karimzadeh 等 - 2018 - FT-IR study and solvent-implicit and explicit effe DOI: 10.1016/j.saa.2018.03.009
• Acetate confidence 1.0

  “peak peak at 1738 for C O stretching gives evidence of carboxylic at 1738 The decrease in the intensity for the peaks at cm-1 cm-1 acid 1505 and ester group present in the hemicellulose, which entirely and 1456 after alkali treatment is a s”

  Kasyapi 等 - 2013 - Bionanowhiskers from jute Preparation and charact DOI: 10.1016/j.carbpol.2012.10.021
• C-S single bond confidence 1.0

  “5B), and shift C-S - (stretch) 1738 1753 1744 [51] (Fig.”

  Probing the interaction of glutathione with different shape of silver-nanoparticles by optical spectroscopy DOI: 10.1016/j.mtcomm.2021.102137
• Carbonyl (C=O) confidence 1.0

  “Camphor and DBP have cm-1 a characteristic carbonyl peak at 1738 and 1720 responding with the main spectral bands for PVAc (1736 cm-1) cm-1) and 1234”

  Identification of cellulose nitrate based adhesive repairs in archaeological pottery of the University of Melbourne’s Middle Eastern archaeological pottery collection using portable FTIR-ATR spectroscopy and PCA DOI: 10.1186/s40494-016-0116-z
• Acetate confidence 1.0

  “However, a distinct containing WPI showed C-O-C glycosidic absorption peak 44o cm-1 Ɵ peak was visible at = in all the hydrogels loaded with at 1167 and C=O stretch for rGO at 1738 cm, conthe drugs (Fig.”

  Owonubi 等 - 2018 - Characterization and in vitro release kinetics of DOI: 10.1007/s40090-018-0139-2