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
478 questions
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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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Why don't equivalent hydrogens cause splitting in NMR?

When doing NMR spectroscopy, it is an observed fact that equivalent hydrogens do not split one another. Why don't equivalent hydrogens split each other's signals? For example, why is the NMR spectrum for ethane a singlet instead of a quartet or even…
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What benefits do higher-rated NMR tubes provide?

You can buy NMR tubes in a huge variety of qualities, with an equally huge difference in price between the cheapest and the most expensive NMR tubes. They are usually rated for a specific spectrometer frequency, e.g. 300 MHz+ or 600 MHz+. What is…
Mad Scientist
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What is the isomer distribution in monosubstituted fluorobullvalene?

Bullvalene (tricyclo[3.3.2.02,8]deca-3,6,9-triene) is a fluxional molecule able to interconvert any two carbon atoms through a series of degenerate Cope rearrangements (for more information, see the Wikipedia article on bullvalene). At slightly…
ron
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Correlation between 1H and 13C shifts - coincidence or not?

A quick glance at any table of typical chemical shifts will reveal that the chemical shifts of protons $(\delta_\mathrm H)$ tend to correlate pretty well with the chemical shifts of the carbons to which they are attached $(\delta_\mathrm C)$. This…
orthocresol
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Multiplet shape in proton NMR of morpholines

I recently carried out a Buchwald–Hartwig reaction to attach a morpholin-4-yl group to an aromatic ring: In the proton NMR of the (columned) product, I found the peaks corresponding to the morpholine protons. The multiplet at 3.86 ppm comes from…
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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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Modern open-source tools for simulation of NMR spectra

I am interested in predicting the NMR spectrum of small organic compounds. It doesn't matter to me if the prediction is very accurate. I'll eventually be comparing the prediction to experimental results. It looks as if several free online tools…
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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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Directionality of ring current-induced magnetic fields in purines

What would be the directions of ring current-induced magnetic fields in purine-like heterocycles in a ​strong magnetic field? Would be the antiparallel state be a default state for these substances in the absence of strong magnetic field at warm…
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Why does the transverse magnetization in Fourier Transform NMR consist of Ix+iIy ($\hat{I}_{\!x}+\mathrm{i}\hat{I}_{\!y}$)?

More specifically, the expression for the average expectation value of the transverse magnetization has the following form: $$M^+(t)=N\gamma \hbar\,\text{Tr}(\hat{\sigma}(t)\hat{F}^+)$$ with $\hat{\sigma}(t)$ the density matrix. $\hat{F}^+$ is…
Jan M.
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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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Why is crystallography still used in some cases for small molecule structure determination?

I was wondering for some time why in some cases x-ray crystallography and not NMR is used for structure determination of small molecules? Does crystallization maybe require a smaller amount of the compound than NMR?
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What is deuterium-depleted water actually used for?

I noted, flipping through the paperback Alfa Aesar catalogue today, that they sell deuterium-depleted water. Under the usage category, they list 'NMR'. I'm trying to work out what specific use this water has. Unfortunately, on the basis of very…
Richard Terrett
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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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