Advanced Topic 921 of 1102 Analytical, Lab & Spectroscopy
NMR Spectroscopy
Nuclei in magnetic fields absorb radio waves, revealing the structure of molecules.
Practise Analytical, Lab & Spectroscopy All Analytical, Lab & Spectroscopy topics
In-depth explanation of NMR Spectroscopy
Nuclear magnetic resonance spectroscopy exploits the fact that nuclei with nonzero spin, such as 1H and 13C, behave as tiny magnets that align in an applied magnetic field. When irradiated with radio frequency energy matching the energy gap between spin states, they absorb and flip, and the resonance frequency depends on the local electronic environment of each nucleus. Analysis of the number of signals, their positions, their intensities and their splitting reveals how many kinds of nuclei are present, their relative numbers and their neighbours. Together these features allow the molecular skeleton to be mapped in detail. NMR is one of the most powerful tools for determining the structure of organic compounds.
Going deeper: NMR Spectroscopy
Key ideas: Resonance frequency is nu = gamma B0/(2 pi), so a 400 MHz instrument has B0 of about 9.4 tesla for protons. Prepare the sample in a deuterated solvent such as CDCl3 so that solvent protons do not swamp the signal, then lock and shim. Count equivalent sets of hydrogens to predict the number of signals. Use D2O exchange to confirm O-H or N-H peaks.
Common mistakes and connections: Students count every hydrogen as a separate signal instead of grouping equivalent ones, forget that molecular symmetry reduces the number of signals, or ignore the residual solvent peak (CHCl3 at 7.26 ppm). Nuclei with even mass and atomic number (12C, 16O) are NMR silent. Higher fields improve resolution but do not change chemical shift in ppm. Links to chemical shift, splitting, integration and 13C NMR.
Visualization of NMR Spectroscopy
Ethanol gives three 1H signals for CH3 near 1.2 ppm, OH near 2.6 ppm and CH2 near 3.7 ppm, one for each kind of hydrogen environment. The interactive lesson shows this as a live animation or chart.
Worked example and use case
The 1H NMR spectrum of ethanol shows three signals, for CH3, CH2 and OH.
Frequently asked questions about NMR Spectroscopy
What is NMR Spectroscopy?
Nuclei in magnetic fields absorb radio waves, revealing the structure of molecules.
Is NMR Spectroscopy a beginner, intermediate or advanced topic?
NMR Spectroscopy is a advanced topic in Analytical, Lab & Spectroscopy. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before NMR Spectroscopy?
Study these earlier topics in Analytical, Lab & Spectroscopy first: Characteristic IR Absorptions, Fingerprint Region, Raman Spectroscopy.
What comes after NMR Spectroscopy?
The next topics in Analytical, Lab & Spectroscopy are Chemical Shift and Spin-Spin Splitting.
Can I practise NMR Spectroscopy with quizzes?
Yes. The interactive lesson includes a self-check question on NMR Spectroscopy, and the Analytical, Lab & Spectroscopy quiz draws on every topic in this area.
Where NMR Spectroscopy fits in Analytical, Lab & Spectroscopy
NMR Spectroscopy is topic 45 of 99 in Analytical, Lab & Spectroscopy.