What absorbs at 3740 cm⁻¹ in an FTIR spectrum?
A band near 3740 cm⁻¹ can point to several functional groups. Below are the most likely assignments, ranked by how much published evidence supports each — every one traceable to literature (DOI) and cross-validated against our 130,000+ reference spectra and knowledge graph.
Backed by 8 cited sources
Quick answer
A band near 3740 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
| Functional group | Supporting facts | Cited sources | Top confidence |
|---|---|---|---|
| Hydroxyl (O-H) | 14 | 10 | 1.0 |
| Silanol (Si-OH) | 12 | 10 | 1.0 |
| Silicon (Si) | 7 | 6 | 1.0 |
| Water (H2O) | 2 | 2 | 1.0 |
| Silicon-oxygen (Si-O) | 2 | 1 | 1.0 |
| Carbon dioxide | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| S s | 1 | 1 | 1.0 |
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 3740 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
“LLM confirmed rule peak-group candidate”
Della Ventura 等 - 2008 - The P2(1)mC2m phase transition in synthetic am DOI: 10.1127/0935-1221/2008/0020-1836 -
S s confidence 1.0
“OAH 3435 76.1 73.4 74.6 72.6 76.4 77.4 79.1 73.5 76.4 stretch 3740 88.1 90.6 89.8 88.3 88.2 89.6 89.9 88.9 89.7 H 2O 3850 88.1 90.6 89.7 88.2 88.3 90.2 90.0 89.5 90.1 S-S stretch (cm(cid:1)1) 2SO Peak 20/1.1 20/1.9 20/2.1 60/1.1 60/1.9 60/2”
Adsorption characteristics of sulfur solution by acticarbon against drinking-water toxicosis DOI: 10.1016/j.sjbs.2016.09.010 -
Hydroxyl (O-H) confidence 1.0
“The FTIR spectrum of cm-1 band is due to residual hydroxyls absorbing about 3505 activated AlBEA sample exhibits IR bands at 3782, 3745, 3740 cm-1”
Penkova 等 - 2007 - Effect of the preparation method on the state of n DOI: 10.1021/jp071927p -
Silanol (Si-OH) confidence 1.0
“cm-1 absorption band centered near 3520 The band at 3740 is assigned to the non-acidic terminal silanol groups (Si OH) cm-1 located on the external surface of the zeolite.”
IR study of iridium bonded to perturbed silanol groups of Pt-HZSM5 for n-pentane isomerization DOI: 10.1016/j.apcata.2011.12.039 -
Silicon (Si) confidence 1.0
“The band at 3740 is assigned to terminal Si-OH groups, and the 27 59 60 cm-1 band at 3780 is due to hydroxyl groups on extra-framework Al oxide.”
Zhao 等 - 2019 - Comparison of Direct, Selective Oxidation of Metha DOI: 10.1021/acs.jpcc.9b04388 -
Silanol (Si-OH) confidence 1.0
“The silanol band around 3740 cm-1 and 977 cm-1 decreased in intensity with higher cycle numbers as TMI”
Synthesis of High Surface Area—Group 13—Metal Oxides via Atomic Layer Deposition on Mesoporous Silica DOI: 10.3390/nano12091458 -
Silanol (Si-OH) confidence 1.0
“growth of that at 3650 and decrease of silanol band at 3740 The last to appear are poorly cm-1, resolved broad bands at 2140-2138 they increase with the growing pressure of CO gas in the cell up to several Torr.”
Belykh 等 - 2019 - Deep insight into CO adsorption on Ni-USY zeolite DOI: 10.1016/j.apcata.2019.117140 -
Hydrogen bond confidence 1.0
“The asymmetric to lower wavenumber of the 2 cm-1 band at 3740 was due to hydrogen bonding and possibly to the presence of terminal TiOH groups located on other planes than (001) [41].”
Unravelling water effects on solid acidic catalysts: Case study of TiO 2 /SiO 2 for dehydration of isobutanol DOI: 10.1016/j.jcat.2016.12.007
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