What absorbs at 1718 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1718 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 1718 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

• Amide confidence 1.0

  “This region cm-1 1H types, the peak around 1718 in 2O is shifted to lower overlaps with the amide I vibrations and is dominated by cm-1 1H/2H wavenumbers by approximately 10 upon excm-1 the large negative difference signal at 1678 (see Figu”

  Haas 等 - 2005 - FTIR difference spectra of Wolinella succinogenes DOI: 10.1021/bi051011d
• Alkyl C-H confidence 1.0

  “follows: 3119 (N-H stretching), 3063, 2898 and 2828 (C-H (C¼O This reveals that the TP-CA cocrystal was formed after cogrinding stretching), 1718 and 1667 stretching bands), 1568 and beyond 50min.”

  Solid-state thermal behavior and stability studies of theophylline–citric acid cocrystals prepared by neat cogrinding or thermal treatment DOI: 10.1016/j.jssc.2012.04.010
• Carbonyl (C=O) confidence 1.0

  “LLM confirmed rule peak-group candidate”

  Lai 和 Wu - 2008 - Investigation on the conformations of AOT in water DOI: 10.1016/j.molstruc.2008.01.017
• Amide confidence 1.0

  “The proposed chemical reactions of JPUA-TDI and 1532 cm-1 and 1718 cm-1 corresponded to amide (-NH) bending and amide (-NH) stretching JPUA-IPDI are illustrated in Figure 4.”

  Mudri 等 - 2020 - Comparative Study of Aromatic and Cycloaliphatic I DOI: 10.3390/polym12071494
• Acetate confidence 1.0

  “224 Presence of C=O and C-O stretch bends in the polymers was supported by the peaks at 1718 225”

  Synthesis, characterization, and application of β-cyclodextrin-based ion-imprinted polymer for selective sequestration of Cr(VI) ions from aqueous media: Kinetics and isotherm studies DOI: 10.1016/j.molliq.2019.111991
• Carbonyl (C=O) confidence 1.0

  “312 this work the sum of the carbonyl peak areas of the acid, ketone, aldehyde and ester groups instead of the height of the absorbance band at 1718 cm-1 was used to calculate the CO-number.”

  Thermo-Oxidative Degradation during Creep Crack Growth of PE-HD Grades as Assessed by FT-IR Spectroscopy DOI: 10.1002/masy.200451327
• Acetate confidence 1.0

  “It can be obviously detected from cm-1 1641cm-1 peaks at 1718 and which could the spectrum that the NH groups appeared at be assigned for the -C=O stretching and C=C cm-1.”

  Salem 和 Salama - 2020 - Developing a New Class of UV-curable Polyurethane DOI: 10.21608/ejchem.2019.14853.1906
• Carboxyl (COOH) confidence 1.0

  “The characteristic absorption band at 1718 cm-1 would be attributed to the esterified carboxyl groups, probably created via a crosslinking cm-1”

  Cellulose‐reinforced starch biocomposite: optimization of the effects of filler and various plasticizers using Design‐Expert method DOI: 10.1002/star.202000028.