Group Frequency
Definition
A characteristic absorption band associated with a specific functional group (carbonyl about 1700 cm-1, hydroxyl 3200 to 3600 cm-1) used to read off structural features at a glance.
- Definition
- Absorption band tied to a specific functional group
- Carbonyl
- About 1700 cm-1
- Hydroxyl
- 3200 to 3600 cm-1
- Use
- Quick structural read of an FTIR spectrum
Common questions
How do analysts use group frequencies without doing a full spectral library match?+
Because a given functional group absorbs in a narrow, well-documented wavenumber range regardless of the rest of the molecule, an analyst can scan a spectrum for these characteristic bands and quickly infer the presence of an alcohol, ketone, ester, or amine before attempting a full compound identification.
Can group frequencies alone confirm what a substance is?+
No. Group frequencies indicate which functional groups are present but many different compounds share the same groups, so they narrow the possibilities rather than confirm an identity. Confirmation still requires matching the full fingerprint region of the spectrum against a reference library.
Related terms
- ATR-FTIR
- Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy: a non-destructive mid-infrared method that analyses a single drop of milk pressed against an ATR crystal....
- Fingerprint Region
- The 1500 to 400 cm⁻¹ stretch of an infrared spectrum where bending and combination bands produce a pattern unique to a given...
- FTIR
- Fourier-transform infrared spectroscopy. A Michelson interferometer modulates all wavelengths simultaneously, the interferogram is Fourier-transformed into the conventional absorbance versus wavenumber spectrum.
- KBr Pellet
- A classical solid sample mode: 1 to 2 mg analyte ground with about 200 mg dry KBr and pressed in a 13...
- Wavenumber
- The reciprocal of wavelength expressed in cm-1, the universal IR axis. Higher wavenumber means higher photon energy. The mid-IR window is 4000...