In nuclear magnetic resonance (NMR) spectroscopy, the chemical shift is the resonant frequency of an atomic nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts are diagnostic of the structure of a molecule. Chemical shifts are also used to describe signals in other forms of spectroscopy such as photoemission spectroscopy.
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. The sample is placed in a magnetic field and the NMR signal is produced by excitation of the nuclei sample with radio waves into nuclear magnetic resonance, which is detected with sensitive radio receivers. The intramolecular magnetic field around an atom in a molecule changes the resonance frequency, thus giving access to details of the electronic structure of a molecule and its individual functional groups. As the fields are unique or highly characteristic to individual compounds, in modern organic chemistry practice, NMR spectroscopy is the definitive method to identify monomolecular organic compounds.
Solid-state NMR (ssNMR) spectroscopy is a technique for characterizing atomic level structure in solid materials e.g. powders, single crystals and amorphous samples and tissues using nuclear magnetic resonance (NMR) spectroscopy. The anisotropic part of many spin interactions are present in solid-state NMR, unlike in solution-state NMR where rapid tumbling motion averages out many of the spin interactions. As a result, solid-state NMR spectra are characterised by larger linewidths than in solution state NMR, which can be utilized to give quantitative information on the molecular structure, conformation and dynamics of the material. Solid-state NMR is often combined with magic angle spinning to remove anisotropic interactions and improve the resolution as well as the sensitivity of the technique.
Carbon-13 (C13) nuclear magnetic resonance is the application of nuclear magnetic resonance (NMR) spectroscopy to carbon. It is analogous to proton NMR and allows the identification of carbon atoms in an organic molecule just as proton NMR identifies hydrogen atoms. 13C NMR detects only the 13
C
isotope. The main carbon isotope, 12
C
is not detected. Although much less sensitive than 1H NMR spectroscopy, 13C NMR spectroscopy is widely used for characterizing organic and organometallic compounds.
Proton nuclear magnetic resonance is the application of nuclear magnetic resonance in NMR spectroscopy with respect to hydrogen-1 nuclei within the molecules of a substance, in order to determine the structure of its molecules. In samples where natural hydrogen (H) is used, practically all the hydrogen consists of the isotope 1H.
Nuclear magnetic resonance spectroscopy of proteins is a field of structural biology in which NMR spectroscopy is used to obtain information about the structure and dynamics of proteins, and also nucleic acids, and their complexes. The field was pioneered by Richard R. Ernst and Kurt Wüthrich at the ETH, and by Ad Bax, Marius Clore, Angela Gronenborn at the NIH, and Gerhard Wagner at Harvard University, among others. Structure determination by NMR spectroscopy usually consists of several phases, each using a separate set of highly specialized techniques. The sample is prepared, measurements are made, interpretive approaches are applied, and a structure is calculated and validated.
The heteronuclear single quantum coherence or heteronuclear single quantum correlation experiment, normally abbreviated as HSQC, is used frequently in NMR spectroscopy of organic molecules and is of particular significance in the field of protein NMR. The experiment was first described by Geoffrey Bodenhausen and D. J. Ruben in 1980. The resulting spectrum is two-dimensional (2D) with one axis for proton (1H) and the other for a heteronucleus, which is usually 13C or 15N. The spectrum contains a peak for each unique proton attached to the heteronucleus being considered. The 2D HSQC can also be combined with other experiments in higher-dimensional NMR experiments, such as NOESY-HSQC or TOCSY-HSQC.
Two-dimensional nuclear magnetic resonance spectroscopy is a set of nuclear magnetic resonance spectroscopy (NMR) methods which give data plotted in a space defined by two frequency axes rather than one. Types of 2D NMR include correlation spectroscopy (COSY), J-spectroscopy, exchange spectroscopy (EXSY), and nuclear Overhauser effect spectroscopy (NOESY). Two-dimensional NMR spectra provide more information about a molecule than one-dimensional NMR spectra and are especially useful in determining the structure of a molecule, particularly for molecules that are too complicated to work with using one-dimensional NMR.
Nuclear magnetic resonance (NMR) in the geomagnetic field is conventionally referred to as Earth's field NMR (EFNMR). EFNMR is a special case of low field NMR.
In vivo magnetic resonance spectroscopy (MRS) is a specialized technique associated with magnetic resonance imaging (MRI).
A nuclear magnetic resonance spectra database is an electronic repository of information concerning Nuclear magnetic resonance (NMR) spectra. Such repositories can be downloaded as self-contained data sets or used online. The form in which the data is stored varies, ranging from line lists that can be graphically displayed to raw free induction decay (FID) data. Data is usually annotated in a way that correlates the spectral data with the related molecular structure.
Phosphorus-31 NMR spectroscopy is an analytical chemistry technique that uses nuclear magnetic resonance (NMR) to study chemical compounds that contain phosphorus. Phosphorus is commonly found in organic compounds and coordination complexes, making it useful to measure 31P NMR spectra routinely. Solution 31P-NMR is one of the more routine NMR techniques because 31P has an isotopic abundance of 100% and a relatively high gyromagnetic ratio. The 31P nucleus also has a spin of 1⁄2, making spectra relatively easy to interpret. The only other highly sensitive NMR-active nuclei spin 1⁄2 that are monoisotopic are 1H and 19F.
Fluorine-19 nuclear magnetic resonance spectroscopy is an analytical technique used to detect and identify fluorine-containing compounds. 19F is an important nucleus for NMR spectroscopy because of its receptivity and large chemical shift dispersion, which is greater than that for proton nuclear magnetic resonance spectroscopy.
Carbohydrate NMR spectroscopy is the application of nuclear magnetic resonance (NMR) spectroscopy to structural and conformational analysis of carbohydrates. This method allows the scientists to elucidate structure of monosaccharides, oligosaccharides, polysaccharides, glycoconjugates and other carbohydrate derivatives from synthetic and natural sources. Among structural properties that could be determined by NMR are primary structure, saccharide conformation, stoichiometry of substituents, and ratio of individual saccharides in a mixture. Modern high field NMR instruments used for carbohydrate samples, typically 500 MHz or higher, are able to run a suite of 1D, 2D, and 3D experiments to determine a structure of carbohydrate compounds.
Nuclear magnetic resonance decoupling is a special method used in nuclear magnetic resonance (NMR) spectroscopy where a sample to be analyzed is irradiated at a certain frequency or frequency range to eliminate fully or partially the effect of coupling between certain nuclei. NMR coupling refers to the effect of nuclei on each other in atoms within a couple of bonds distance of each other in molecules. This effect causes NMR signals in a spectrum to be split into multiple peaks. Decoupling fully or partially eliminates splitting of the signal between the nuclei irradiated and other nuclei such as the nuclei being analyzed in a certain spectrum. NMR spectroscopy and sometimes decoupling can help determine structures of chemical compounds.
Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at the nucleus. This process occurs near resonance, when the oscillation frequency matches the intrinsic frequency of the nuclei, which depends on the strength of the static magnetic field, the chemical environment, and the magnetic properties of the isotope involved; in practical applications with static magnetic fields up to ca. 20 tesla, the frequency is similar to VHF and UHF television broadcasts (60–1000 MHz). NMR results from specific magnetic properties of certain atomic nuclei. Nuclear magnetic resonance spectroscopy is widely used to determine the structure of organic molecules in solution and study molecular physics and crystals as well as non-crystalline materials. NMR is also routinely used in advanced medical imaging techniques, such as in magnetic resonance imaging (MRI).
Sodium hexachloroplatinate(IV), the sodium salt of chloroplatinic acid, is an inorganic compound with the formula Na2[PtCl6], consisting of the sodium cation and the hexachloroplatinate anion. As explained by Cox and Peters, anhydrous sodium hexachloroplatinate, which is yellow, tends to form the orange hexahydrate upon storage in humid air. The latter can be dehydrated upon heating at 110 °C.
Nucleic acid NMR is the use of nuclear magnetic resonance spectroscopy to obtain information about the structure and dynamics of nucleic acid molecules, such as DNA or RNA. It is useful for molecules of up to 100 nucleotides, and as of 2003, nearly half of all known RNA structures had been determined by NMR spectroscopy.
Paramagnetic nuclear magnetic resonance spectroscopy refers to nuclear magnetic resonance (NMR) spectroscopy of paramagnetic compounds. Although most NMR measurements are conducted on diamagnetic compounds, paramagnetic samples are also amenable to analysis and give rise to special effects indicated by a wide chemical shift range and broadened signals. Paramagnetism diminishes the resolution of an NMR spectrum to the extent that coupling is rarely resolved. Nonetheless spectra of paramagnetic compounds provide insight into the bonding and structure of the sample. For example, the broadening of signals is compensated in part by the wide chemical shift range (often 200 ppm in 1H NMR). Since paramagnetism leads to shorter relaxation times (T1), the rate of spectral acquisition can be high.
Nitrogen-15 nuclear magnetic resonance spectroscopy is a version of nuclear magnetic resonance spectroscopy that examines samples containing the 15N nucleus. 15N NMR differs in several ways from the more common 13C and 1H NMR. To circumvent the difficulties associated with measurement of the quadrupolar, spin-1 14N nuclide, 15N NMR is employed in samples for detection since it has a ground-state spin of ½. Since14N is 99.64% abundant, incorporation of 15N into samples often requires novel synthetic techniques.
