What absorbs at 1644 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 1644 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.

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 1644 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

  “r ip cm-1 Since a dramatic decrease in intensity was observed for the 1644 band, and not the other t cm-1 Amide I bands, the intensity at 1644 was monitored during the thermal transition, and showed excellent agreement with the CD melting c”

  Bryan 等 - 2007 - FTIR studies of collagen model peptides Complemen DOI: 10.1021/ja071154i.
• Acetate confidence 1.0

  “1425, 780 W-DO had characteristic peaks at 1723(C=O vibration), 1644, 1420, 1396, 1378, cm-1 1339, 1248, 1227, 1158,1103, 1074, 775 and 713 corresponding to the characteristic peaks of cm-1.”

  Discrimination and similarity evaluation of tissue-cultured and wild Dendrobium species using Fourier Transform Infrared Spectroscopy DOI: 10.1016/j.molstruc.2015.01.027
• Amide confidence 1.0

  “(1645cm-1) a 5.388a,b b Peak position Amide I 1644.08 ± 7.714 1645.35 ± 1649.87 ± 6.286 (3456cm-1) a”

  Plasma membrane proteins_ A new probe for the characterization of breast cancer DOI: 10.1016/j.lfs.2019.116777
• Amide confidence 1.0

  “placenta, from in figure 6, after eight weeks of growth, shows splitting into three bands, suggesting cm-1, cm-1 cm-1 α-helices occurrence of at 1654 disordered amide I band at 1644 and ß sheet at 1625”

  Gupta 等 - 2022 - In vitro cell composition identification of wood d DOI: 10.1098/rsos.201935
• Acetate confidence 1.0

  “NH3+ 1520 1520 1520 1520 [54] Overall, it can be observed that the response of the AS peak height 1644 1629 C--O Amide (stretch) 1651 1692 [53] 1685 1640”

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

  “Band at 1644 associated with OH bending due to absorption of water [13].”

  Microencapsulation of ginger-based essential oil (Zingiber cassumunar roxb) with chitosan and oil palm trunk waste fiber prepared by spray-drying method DOI: 10.1016/j.csite.2020.100606
• Amide confidence 1.0

  “The peaks at 1644 and cm-1 1640 represent the characteristic peak of C = O stretching vibration of the amide I band of non-infected 24 h 4b)44.”

  Antimicrobial potential of a ponericin-like peptide isolated from Bombyx mori L. hemolymph in response to Pseudomonas aeruginosa infection DOI: 10.1038/s41598-022-19450-8
• Hydroxyl (O-H) confidence 1.0

  “The first broad and weak peak at 1644 due to O-H deformation (Druliolle et al., 1997).”

  Pappas 等 - 2008 - Identification and differentiation of goat and she DOI: 10.1016/j.foodchem.2007.07.034