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High-Temperature and High-Pressure In situ Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy
Published on: October 9, 2020
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TEMPO in Solution, Melted, Solid, and Adsorbed on a Silica Surface: A Paramagnetic NMR Study.
Ehsan Shakeri1, Gabrielle E Harmon-Welch1, Sara A C MacWade1
1Department of Chemistry, Texas A&M University, Texas, USA.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|November 30, 2025
Summary
Paramagnetic Nuclear Magnetic Resonance (NMR) spectra of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) reveal all 1H and 13C signals. This stable radical exhibits distinct chemical shifts and linewidths in solution and solid states.
Area of Science:
- Chemistry
- Spectroscopy
- Materials Science
Background:
- TEMPO (2,2,6,6-tetramethyl-1-piperinyloxy) is a stable radical with applications in synthesis, catalysis, and as a spin probe.
- Previous studies extensively utilized Electron Paramagnetic Resonance (EPR) for TEMPO analysis.
- The Nuclear Magnetic Resonance (NMR) properties of TEMPO remained largely unreported.
Purpose of the Study:
- To report the paramagnetic NMR properties of TEMPO for the first time.
- To investigate the influence of TEMPO on solvent and other molecule NMR signals.
- To explore TEMPO's behavior in different states (solution, molten, adsorbed).
Main Methods:
- Paramagnetic 1H and 13C NMR spectroscopy of TEMPO in various solvents and concentrations.
- Investigation of TEMPO's effect on solvent chemical shifts and 31P NMR of PPh3.
- Paramagnetic solid-state NMR to study TEMPO adsorbed on a silica surface.
Main Results:
- All 1H and 13C NMR signals of TEMPO were observed in paramagnetic NMR spectra.
- 1H NMR spectra showed a 50 ppm chemical shift range (8 scans), and 13C NMR signals appeared within 30 minutes (2600 ppm range).
- Solvents exhibited chemical shift changes; adduct formation occurred with CDCl3. Higher TEMPO concentrations narrowed signals, with molten TEMPO showing the most significant effect. Solid-state NMR confirmed TEMPO adsorption on silica.
Conclusions:
- Paramagnetic NMR is a viable technique for characterizing TEMPO.
- TEMPO significantly influences the NMR spectra of its environment, including solvents and other molecules.
- TEMPO retains solution-like NMR characteristics when adsorbed on surfaces.
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