January 25, 2024
by Sarah Srokosz, Marketing Communications Specialist, ACD/Labs
A Guide to Understanding NMR Abbreviations
In addition to the complex terminology that is used to communicate the world of NMR spectroscopy, scientists and researchers in this space also find themselves immersed in a world of seemingly countless acronyms. Experts in the field use these acronyms broadly to describe anything from specialized pulse sequences to even just the name of the underlying phenomenon itself.
For non-experts and those entering the field for the first time, deciphering the acronyms can feel akin to learning a secret language. In the worst-case scenario, this unnecessary obstacle may inhibit access to the wealth of information that NMR data can offer.
In this blog post, we embark on a journey to demystify the enigmatic world of NMR acronyms. Whether you’re a seasoned NMR spectroscopist seeking a reminder about an unfamiliar experiment, or a curious mind entering the field of NMR, use this post as your guide. As we break these acronyms down, we include the meaning behind them to deepen your understanding and make them easier to recall in the future.
The Glossary of NMR Acronyms
With the breadth and ever-expanding nature of the field of NMR, it is nearly impossible to fit an exhaustive list into a single post. However, this curated list of essential acronyms stands to help NMR spectroscopists and enthusiasts across a variety of industries and applications.
For ease of navigation, we’ve separated out the acronyms into two groups; those used generally within the field, and those that serve as names of specific experiments. Each group is arranged in alphabetical order.
General NMR Acronyms
| Acronym | Expansion | Meaning |
| CW(NMR) | Continuous Wave (NMR) | The predecessor of FTNMR, CWNMR irradiated a sample with a continuous radio frequency (RF) signal while detecting how much of it was absorbed, and the spectrum was generated by sweeping across small changes in the magnetic field. |
| EPR | Electron paramagnetic resonance | A method for studying materials with unpaired electrons analogous to NMR, but the excited spins are those of the electrons instead of the atomic nuclei, also referred to as electron spin resonance (ESR). |
| FFT | Fast Fourier transform | A Fourier transform algorithm which reduces the complexity of the operation by reducing the number of computations involved. This drastically reduces the amount of time needed for signal processing and can even provide more accurate results. |
| FID | Free induction decay | The transient electromagnetic signal generated by non-equilibrium nuclear spins precessing about the magnetic field. In FTNMR, this is the observable NMR signal that results after the nuclear spins are perturbed by the RF pulse. |
| FT | Fourier transform | A mathematical operation that converts a function in the time domain to one in the frequency domain. The Fourier transform is analogous to decomposing the sound of a musical chord into terms of the intensity of its constituent pitches. |
| GARP | Globally optimized alternating phase rectangular pulse | Pulse sequence used for heteronuclear decoupling of nuclei with wide chemical shift regions without resulting in distorted line shapes that would otherwise be obtained with broadband decoupling. |
| MLEV | Malcolm Levitt (composite pulse decoupling sequence) | A sequence of composite pulses designed to remove signal splitting in multinuclear NMR experiments due to homonuclear J-couplings. It is also used to allow magnetization transfer via isotropic mixing. |
| MRI | Magnetic resonance imaging | A medical imaging technique that uses nuclear magnetic resonance signals and pulsed field gradients to generate images of live tissue. |
| NMR | Nuclear magnetic resonance | The physical phenomenon in which nuclei with a magnetic moment (e.g., 1H or 13C) selectively absorb high-frequency radio waves characteristic of the magnetic field at the nucleus while in the presence of a strong constant magnetic field. |
| NOE | Nuclear Overhauser effect | A spin relaxation phenomenon in which the spin population differences of neighbouring (4-5 Å) spins are altered from their equilibrium values, giving rise to changes in the intensities of NMR resonances of spins, and providing information about 3D structure and conformation. |
| NUS | Non-uniform sampling | A method of reducing experiment time in multidimensional NMR experiments by collecting only a portion of data in the indirect dimension, which is then reconstructed by a mathematical algorithm to give results comparable to those obtained by the full experiment. |
| PFG | Pulsed field gradient | The application of a short (pulsed) magnetic field gradient across the sample, which “defocuses” spins of a given nuclei, resulting in zero net magnetization. This technique allows spectroscopists to selectively supress or refocus certain resonances. Many modern experiments employ this technique and are referred to as “gradient-selected”, “gradient-enhanced”, or simply “gradient” experiments. |
| RDC | Residual dipolar coupling | The small dipolar coupling between two nuclear spins remaining when the sample is dissolved in a partially oriented medium, which does not allow the dipolar couplings to completely cancel because of free motion and rotation. The measurement of these can provide 3D structural information. |
| RF | Radio frequency | The oscillation rate of an electromagnetic field in the frequency range from around 20 kHz to 300 GHz. In NMR, the weak oscillating magnetic field component that perturbs the aligned magnetic nuclear spins is usually referred to as an RF pulse. |
| WALTZ | Wideband alternating-phase low-power technique for zero residual splitting | A sequence of composite pulses applied repeatedly; designed to remove signal splitting in multinuclear NMR experiments due to heteronuclear J-couplings. |
NMR Experiment Acronyms
| Acronym | Expansion | Meaning |
| ADEQUATE | Adequate sensitivity double–quantum transfer experiment | Type: 2D
Relevant Nuclei: 1H and 13C, usually What It Does: Correlates coupled carbon pairs (double quantum frequency) to proton chemical shifts Purpose: Provides carbon-carbon connectivity information with better sensitivity than INADEQUATE |
| COSY | Correlation spectroscopy | Type: 2D
Relevant Nuclei: Typically 1H, but can be done for other high-abundance spins, such as 31P, 19F, 11B, etc. What It Does: Correlates chemical shifts of the nuclei in question Purpose: Reveals which nuclei are coupled to each other |
| DEPT | Distortionless enhancement by polarization transfer | Type: 1D
Relevant Nuclei: Typically 13C What It Does: Transfers polarization from an excited nucleus to another (most commonly 1H→13C) Purpose: Provides selective sensitivity enhancement relative to the standard decoupled 1D spectra as well as information about the multiplicity of the carbon atoms |
| DOSY | Diffusion ordered spectroscopy | Type: Pseudo-2D
Relevant Nuclei: Any NMR-active nuclei What It Does: Measures the apparent diffusion coefficients of nuclear spins using pulsed field gradients and appropriately designed pulse sequences Purpose: Generates a pseudo-2D spectrum where the Y axis is the diffusion coefficient and the nuclear spins are arranged in lines according to their specific diffusion rates, which can be used to distinguish components of a mixture or gain insight into the MW of the components based on their hydrodynamic volume |
| EXSY | Exchange spectroscopy | Type: 2D
Relevant Nuclei: Any NMR-active nuclei, the ones with higher abundance are preferred What It Does: It correlates nuclear spins that are associated via chemical exchange Purpose: Identifies the chemical species that undergo exchange in the NMR experiment timeframe, can be intramolecular (e.g., rotation around an amide bond) or intermolecular (e.g., exchange of a labile proton with water) |
| HEHAHA | Heteronuclear Hartmann-Hahn (spectroscopy) | Type: 2D
Relevant Nuclei: Any two different NMR-active nuclei with 100% abundance What It Does: Transfers magnetization successively between nuclei up to 6 or more bonds away, as long as successive spins are coupled Purpose: Reveals scalar couplings amongst all nuclei in a spin system, as opposed to only those that are directly coupled, like in COSY. Can reveal the complete spin/coupling network of a particular nucleus, i.e., all the signals of a particular amino acid in a peptide or protein. |
| HETCOR | Heteronuclear correlation Spectroscopy | Type: 2D
Relevant Nuclei: Any two different NMR-active nuclides, usually a sensitive and an insensitive one, typically 1H and 13C What It Does: Correlates chemical shifts of two different nuclei that are (usually) directly bonded Purpose: Identifies 1-bond heteronuclear through-bond couplings, though may suffer from low sensitivity as it directly detects the insensitive nucleus |
| HMBC | Heteronuclear multiple bond correlation/coherence | Type: 2D
Relevant Nuclei: Any two different NMR-active nuclei, though typically 1H and 13C What It Does: Correlates chemical shifts of two different nuclei separated from each other by two or more (typically 2–3) bonds and coupled to each other Purpose: Identifies heteronuclear through-bond couplings that are generally not observable in other NMR experiments due to the scalar coupling constants being smaller (<10 Hz) than the typically observed linewidths |
| HMQC | Heteronuclear multiple quantum correlation/coherence | Type: 2D
Relevant Nuclei: Any two different NMR-active nuclei, though typically 1H and 13C or 15N What It Does: Correlates chemical shifts of two different nuclei that are directly bonded Purpose: Identifies 1-bond heteronuclear through-bond coupling with greater sensitivity than HETCOR (due to detection of the sensitive nucleus), though observed signals tend to be broad, since it measures the multiple quantum coherences |
| HOESY | Heteronuclear Overhauser effect spectroscopy | Type: 2D
Relevant Nuclei: Any two different NMR-active nuclides, though typically one is 1H What It Does: Detects the transfer of nuclear spin polarisation from one nucleus to the other Purpose: Detects (and under some conditions quantifies) both through-bond and through-space (nuclear Overhauser) effects between two different nuclei in close proximity in three-dimensional space (typically < 5 Å) |
| HOHAHA | Homonuclear Hartmann-Hahn (spectroscopy) | Another name for TOCSY |
| HSQC | Heteronuclear single quantum correlation | Type: 2D
Relevant Nuclei: Any two different NMR active nuclei, though typically 1H and 13C or 15N What It Does: Correlates chemical shifts of two different nuclei that are directly bonded Purpose: Identify 1-bond heteronuclear through-bond couplings with higher resolution than the HMQC, since it measures the single quantum coherence magnetization transfer |
| INADEQUATE | Incredible natural abundance double quantum transfer experiment | Type: 2D
Relevant Nuclei: Usually 13C, but other examples have been reported What It Does: Correlates coupled carbon pairs through detected double quantum transitions Purpose: Reveals 1-bond carbon-carbon through-bond couplings but is limited by the very low abundance of 13C-13C pairs |
| INEPT | Insensitive nuclei enhanced by polarization transfer | Type: 1D, but often incorporated into other 2D experiments
Relevant Nuclei: NMR-active insensitive nuclei, usually with low gyromagnetic ratios (γ), such as 15N or 13C What It Does: Transfers the greater population differences of a high-γ nucleus (such as 1H, 19F, or 31P) nucleus onto the coupled less-sensitive nucleus of interest Purpose: Enhance the sensitivity of the 1D spectrum of the insensitive nucleus |
| NOESY | Nuclear Overhauser effect spectroscopy | Type: 2D
Relevant Nuclei: Any NMR-active nucleus What It Does: Detects the transfer of nuclear spin polarisation from one nucleus to the other of the same type Purpose: Detects (and under some conditions quantifies) both through-bond and through-space (nuclear Overhauser) effects between two nuclei in close proximity in three-dimensional space (typically < 5 Å) |
| ROESY | Rotational nuclear Overhauser effect spectroscopy | Type: 2D
Relevant Nuclei: Any NMR-active nucleus What It Does: Measures NOEs in the “rotating frame” by focusing on the interactions between a selected nucleus and all other nuclei of the same type in the molecule Purpose: Maps NOE correlations for mid-sized molecules (1000–3000 Da) that have close to zero conventional NOEs |
| SECSY | Spin echo correlated spectroscopy | Type: 2D
Relevant Nuclei: Any NMR-active nucleus What It Does: Correlates chemical shifts of the nuclei in question Purpose: Reveals homonuclear couplings using a smaller data set, making it particularly suitable for studies of macromolecules |
| TOCSY | Total correlated spectroscopy | Type: 2D
Relevant Nuclei: Any NMR-active nucleus with 100% abundance What It Does: Transfers magnetization successively between nuclei up to 6 or more bonds away, as long as successive spins are coupled Purpose: Reveals scalar couplings amongst all nuclei in a spin system (up to the complete spin/coupling network of a particular nucleus, i.e., all the signals of a particular amino acid in a peptide or protein) as opposed to only those that are directly coupled, like in COSY |
NMR Jargon Can Be Difficult, but Your Data Analysis Doesn’t Have to Be
As you gain experience in the field of NMR spectroscopy, you quickly find that not all NMR data processing software is created equal. Instrument vendor software is primarily designed for acquisition workflows. So when it comes to data processing, you may find this software difficult to use or unreliable. In the case of complex experiments, it may not even contain the algorithms or tools you need to extract valuable information from your data. Third-party software on the other hand, is designed with processing and analysis at the forefront.
Like this blog post, ACD/Labs is also working to relieve scientists of unnecessary burdens. Our portfolio of software for NMR data analysis is backed by nearly three decades of experience in providing state-of-the-art tools, including our industry-leading NMR predictors, as well as the most peer-reviewed computer-assisted structure elucidation (CASE) system on the market. Our software portfolio offers applications for everyone in the spectroscopy industry, regardless of their industry or experience level, whether they’re interested in structure elucidation, verification, or quantitation. To further simplify your workflows, it also allows you to process and interpret all your other analytical data in the same place.
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