How do ultraviolet spectroscopy, infrared spectroscopy, magnetic resonance, and mass spectrometry help study reaction mechanisms?

In the study of reaction mechanisms, chemists rely on sensitive instrumental techniques to identify transient intermediates and define the stages of a reaction. Ultraviolet, infrared, magnetic resonance, and mass spectrometry are essential tools for this purpose.1

• Ultraviolet (UV) Spectroscopy: Often used to observe electronic spectra, UV spectroscopy helps monitor molecules excited to higher energy states. It is particularly valuable for observing short-lived reaction intermediates, which can be trapped at low temperatures to facilitate analysis.2
• Infrared (IR) Spectroscopy: By measuring the stretching and bending vibrations of chemical bonds, IR spectroscopy provides detailed structural data. It allows researchers to identify specific functional groups present in molecules, which is critical for tracking how reactants transform into products.34
• Magnetic Resonance: Techniques such as nuclear magnetic resonance (NMR) probe molecular structure by observing how nuclei respond to magnetic fields and radio waves. These methods are increasingly used to investigate rapid energy transfers and the elementary steps of complex reactions.5
• Mass Spectrometry: This technique identifies and quantifies intermediate species as a function of time, helping to resolve reaction kinetics. Through isotopic labeling, researchers can track the movement of specific atoms during a reaction, clarifying whether processes are intramolecular or intermolecular.61