Questions tagged [nmr-spectroscopy]

This tag should be applied to all questions about nuclear magnetic resonance, including the underpinning theory and the measurement or interpretation of spectra.

Nuclear magnetic resonance (NMR) is a spectroscopic method used for the determination of the structures of molecules containing NMR-active nuclei, and may also be used as a method for studying mechanisms of chemical reactions.

Unlike methods such as IR spectroscopy or UV-vis spectroscopy, NMR is a quantitative technique that gives structural information such as the number of nuclei present, and the way in which they couple to one another, with a vast number of different NMR experiments available to probe various properties of the molecule of interest.

Though initially a technique for small molecule elucidation in organic chemistry, advances in technology have allowed the application of NMR to large biological molecules such as proteins, and gave rise to the related MRI (magnetic resonance imaging) which is widely used in medicine as a means of imaging the body.

Definition:

Wikipedia:

Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a magnetic field absorb and re-emit electromagnetic radiation. This energy is at a specific resonance frequency which depends on the strength of the magnetic field and the magnetic properties of the isotope of the atoms; in practical applications, the frequency is similar to VHF and UHF television broadcasts (60–1000 MHz). NMR allows the observation of specific quantum mechanical magnetic properties of the atomic nucleus. Many scientific techniques exploit NMR phenomena to study molecular physics, crystals, and non-crystalline materials through nuclear magnetic resonance spectroscopy. NMR is also routinely used in advanced medical imaging techniques, such as in magnetic resonance imaging (MRI).

Applicability of the tag:

  • should be applied to all questions that deal with nuclear magnetic resonance, including…
    • Theory questions about the theoretical chemistry behind the method, or about the way in which pulse sequences work
    • Practical questions about the measurement of NMR spectra, choice of techniques, instrumentation
    • Questions about the application of NMR, for instance in structure elucidation
  • The majority of questions will need additional tags to fully describe them, for instance if the question is asking about the NMR spectrum of a particular organic molecule or if the question is asking about the physical basis for why the technique works.
    • The tag should also be applied to allow for easier searching, in the same way that a question might have tags for and .
    • The tag may also be appropriate, but is perhaps best reserved for questions specifically regarding general analytical methods rather than for specific techniques.

Related tags:

The following tags are related to , with multiple questions on chemistry.se already tagged with one of more of the following:

Further reading:

Many books/reviews on NMR have been published from theoretical and practical perspectives. A selection of the more approachable books aimed at chemists are:

  • Keeler, J; Understanding NMR Spectroscopy;S Wiley-Blackwell: Sussex, 2010.
  • Claridge, T. D. W. ; High Resolution NMR Techniques in Organic Chemistry; Elsevier: Oxford, 2009
  • Levitt, M. H.; Spin Dynamics: Basics of Nuclear Magnetic Resonance; Wiley: Sussex, 2008
  • Macomber, R. S.; A Complete Introduction to Modern NMR Spectroscopy; Wiley-Interscience: New York, 1998
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Splitting of multiplets in ¹H NMR spectra?

I'm currently taking VCE (Victorian Certificate of Education) Chemistry classes, and we're currently studying the interpretation of spectra produced by Hydrogen NMR (Nuclear Magnetic Resonance) spectroscopy. When studying the spectra of High…
Anti Earth
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What are the differences between the HMQC and HSQC experiments?

This afternoon, I was having some trouble with an HSQC (Heteronuclear Single Quantum Coherence Spectroscopy) spectrum I was trying to acquire, and the spectroscopist recommended I try HMQC (Heteronuclear Multiple Quantum Coherence) spectra, as they…
Canageek
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What factors are important for quantitative analysis of a proton 1D-NMR spectrum?

Besides elucidating or verifying a chemical structure, NMR can also be used e.g. for quantifying a mixture of different chemicals. Depending on the quality of the spectrum and the specific substance, integrating the NMR signals for the same…
Mad Scientist
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Where does magnetic inequivalence come from?

As the question says, I'm having trouble understanding where does magnetic inequivalence in $\ce{^1H}$ NMR come from. All the sources I've found say that two protons are magnetically equivalent if all $J$ values to all other spins in the molecule…
ralk912
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Qualitative explanation of how COSY works

I think I understand 1D Proton NMR with the Fourier Transform, qualitatively. However, I am struggling to understand 2D COSY NMR. I am stuck on a few things; In 1D Proton FT-NMR, the "Pulse" I understand to be the application of a transverse…
Mark R
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Comparison of COSY and TOCSY for detection of small couplings between protons

I routinely run COSY spectra to help with assignment of my proton NMR. The experiment is fast to run and generally useful, however some of the intermediates I've recently been making have had sufficiently small coupling constants that the COSY…
NotEvans.
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Why do aromatic hydrogen atoms have a higher chemical shift value compared to aliphatic hydrogen atoms?

In Nuclear magnetic resonance (H-NMR) spectroscopy, the chemical shift of aliphatic hydrogen atoms are very much closer to the 1.0 ppm than that of aromatic hydrogen atoms. Aromatic hydrogen atoms have a chemical shift value of about 7.0-9.0 ppm…
jokerdino
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Is there a real detection limit in NMR spectroscopy?

From what I've read, my impression is that with a sufficient number of scans etc., one can get spectra from even very dilute samples (S:N ratio ~ $\sqrt{\text{NS}}$). Obviously, this is not always possible in practice and it is not necessarily…
orthocresol
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Why do electronegative atoms depress coupling constants?

Related to this previous question about detection of small couplings between protons. In a recent conversation with our labs NMR technician, it was stated that coupling constants decrease in the presence of electronegative atoms: ...and you…
NotEvans.
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Sources for raw 1H-NMR data?

Where can one find examples of raw data for an 1H-NMR spectrum? This may sound as an odd request, so I'll give some context. I have found lots of images of spectra such as this: where you can see an image of the peaks. What I am interested is a…
soegaard
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Nitrobenzene and other monosubstituted benzenes 1H vs 13C NMR assignments

The reported 1H NMR spectrum for nitrobenzene has three signals corresponding to H2/H6, H3/H5 and H4, respectively. The signals (ppm) appear at 8.25 (H2/H6), 7.71 (H4), and 7.56 (H3/H5). This is, the ortho protons are the most deshielded, followed…
ralk912
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Why is proton coupling through bonds and how does this affect identical protons?

I had the opportunity to work with a NMR spectrometer and decided to learn some of the theory behind it. After finishing Clayden's chapter on $^{1}\textrm{H}$ NMR (Ch. 11) I'm still left with some questions, mostly concerning coupling. Proton…
Jori
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Can non-deuterated solvents be used for 13C-NMR (and in fact other nuclei)?

Basically, my question is can you used a non-deuterated solvent for 13C NMR? I'm thinking that there might be some problems with locking?
123456789
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Can a NOESY NMR experiment be halted partway through and give meaningful results?

Some NMR experiments can be halted partway through the acquisition and still give perfectly valid results: The traditional 1H experiment for example. Others, like a Saturation Transfer Difference Spectrum will have errors in the magnitude of the…
Canageek
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What is the origin of 'tenting' or 'roofing' in NMR spectra?

Given an NMR spectrum with two coupled nuclei one can often observe so-called 'roofing' – an asymmetry in the multiplet. For example, here is a 300 MHz proton spectrum of 1-bromo-2-methoxyethane, where the inset shows the triplets corresponding to…
Paweł Tokarz
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