I

Infrared Spectroscopy

IR: 4000–400 cm⁻¹; C=O at ~1720 cm⁻¹
AllChemicals — The Online Chemical Glossary | https://allchemicals.info/chemical/514-infrared-spectroscopy
Quick Reference
Formula / NotationIR: 4000–400 cm⁻¹; C=O at ~1720 cm⁻¹
Also Known AsIR spectroscopy, infrared spectroscopy, FTIR, Fourier transform infrared spectroscopy

What is Infrared Spectroscopy?

A technique that measures the absorption of infrared radiation by molecules, causing vibrational and rotational transitions. Different functional groups absorb at characteristic frequencies, making IR spectroscopy useful for identifying functional groups and elucidating molecular structure.

Formula & Notation

IR: 4000–400 cm⁻¹; C=O at ~1720 cm⁻¹

Other Names / Synonyms: IR spectroscopy, infrared spectroscopy, FTIR, Fourier transform infrared spectroscopy

Properties & Characteristics

Infrared (IR) spectroscopy measures the absorption of infrared radiation by molecules, causing vibrational transitions (stretching and bending). Only vibrations that change the dipole moment are IR-active. The IR spectrum is a fingerprint of a molecule. Key group frequencies: O-H stretch (2500-3500 cm⁻¹ broad), N-H stretch (~3300-3500 cm⁻¹), C-H stretch (~3000 cm⁻¹), C=O stretch (~1680-1720 cm⁻¹), C=C stretch (~1620-1680 cm⁻¹), C-O stretch (~1000-1300 cm⁻¹). The fingerprint region is 400-1500 cm⁻¹.

Uses & Applications

IR spectroscopy is used in: routine characterisation of organic compounds, qualitative and quantitative analysis, monitoring reactions in situ (ATR-FTIR), environmental monitoring of atmospheric greenhouse gases (CO₂, CH₄, N₂O), quality control of pharmaceuticals, food analysis, and forensic identification of unknown substances.

Safety Information

FTIR instruments use infrared radiation (non-ionising, but intense IR can heat tissue). MCT detectors require liquid nitrogen (cryogenic burns). ATR accessories use hard diamond or ZnSe crystals (ZnSe is toxic). Sample preparation for KBr pellets uses a hydraulic press (pressure hazard). Always wear eye protection when operating IR sources.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Infrared Spectroscopy
Formula IR: 4000–400 cm⁻¹; C=O at ~1720 cm⁻¹
Index All "I" terms
Synonyms IR spectroscopy, infrared spectroscopy, FTIR, Fourier transform infrared spectroscopy

Frequently Asked Questions

A technique that measures the absorption of infrared radiation by molecules, causing vibrational and rotational transitions. Different functional groups absorb at characteristic frequencies, making IR spectroscopy useful for identifying functional groups and elucidating molecular structure.

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AllChemicals.info — The Online Chemical Glossary | https://allchemicals.info/chemical/514-infrared-spectroscopy

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