Variation in resonant frequency of identical atomic nuclei in a magnetic field
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.[1][2][3] Chemical shifts are also used to describe signals in other forms of spectroscopy such as photoemission spectroscopy.
Some atomic nuclei possess a magnetic moment (nuclear spin), which gives rise to different energy levels and resonance frequencies in a magnetic field. The total magnetic field experienced by a nucleus includes local magnetic fields induced by currents of electrons in the molecular orbitals (electrons have a magnetic moment themselves). The electron distribution of the same type of nucleus (e.g. 1H, 13C, 15N) usually varies according to the local geometry (binding partners, bond lengths, angles between bonds, and so on), and with it the local magnetic field at each nucleus. This is reflected in the spin energy levels (and resonance frequencies). The variations of nuclear magnetic resonance frequencies of the same kind of nucleus, due to variations in the electron distribution, is called the chemical shift. The size of the chemical shift is given with respect to a reference frequency or reference sample (see also chemical shift referencing), usually a molecule with a barely distorted electron distribution.
^Silverstein; Bassler; Morrill (1981). Spectrometric Identification of organic Compounds (4th ed.). ISBN 978-0-471-09070-0.
^Kemp, William (1987). Organic Spectroscopy (3rd ed.). ISBN 978-0-333-41767-6.
^Balei, Metin. Basic 1H and 13C-NMR spectroscopy. ISBN 978-0-444-51811-8.
chemicalshift is the resonant frequency of an atomic nucleus relative to a standard in a magnetic field. Often the position and number of chemical shifts...
called the "chemicalshift" with units of parts per million. The chemicalshift provides structural information. The conversion of chemicalshifts (and J's...
being chemically equivalent, giving one single signal, used to define a chemicalshift = 0 ppm. It is volatile, making sample recovery easy as well. Modern...
amenable to analysis and give rise to special effects indicated by a wide chemicalshift range and broadened signals. Paramagnetism diminishes the resolution...
are relevant to NMR spectroscopy, as they dramatically influence the chemicalshifts of 1H nuclei ("protons") in aromatic molecules. The effect helps distinguish...
The chemicalshift index or CSI is a widely employed technique in protein nuclear magnetic resonance spectroscopy that can be used to display and identify...
tumbling" averages out the chemicalshift anisotropy (CSA). In this case, the "average" chemicalshift (ACS) or isotropic chemicalshift is often simply referred...
experiences a distinct electronic environment and thus has a distinct chemicalshift by which it can be recognized. However, in large molecules such as proteins...
Residual chemicalshift anisotropy (RCSA) is the difference between the chemicalshift anisotropy (CSA) of aligned and non-aligned molecules. It is normally...
Protein chemicalshift prediction is a branch of biomolecular nuclear magnetic resonance spectroscopy that aims to accurately calculate protein chemical shifts...
Electrical resonance Quartz thermometer Nuclear magnetic resonance Chemicalshift is temperature dependent. This property is used to calibrate the thermostat...
main areas, nuclear magnetic resonance and the chemicalshift, boron chemistry and the nature of the chemical bond, and large biochemical molecules. These...
system like the chemicalshift or the electric quadrupole interaction can be helpful as well, and in some cases solely the chemicalshift has been employed...
NMR signals, owing to a difference in either chemicalshift (magnetic inequivalence by the chemicalshift criterion) or spin-spin coupling (J-coupling)...
carbohydrate compounds. Common chemicalshift ranges for nuclei within carbohydrate residues are: Typical 1H NMR chemicalshifts of carbohydrate ring protons...
Tetramethylsilane is the accepted internal standard for calibrating chemicalshift for 1H, 13C and 29Si NMR spectroscopy in organic solvents (where TMS...
nuclei with respect to the applied magnetic field determines their chemicalshift. In this context, anisotropic systems refer to the electron distribution...
field. Three main interactions responsible in solid state NMR (dipolar, chemicalshift anisotropy, quadrupolar) often lead to very broad and featureless NMR...
In spectroscopy, bathochromic shift (from Greek βαθύς (bathys) 'deep', and χρῶμα (chrōma) 'color'; hence less common alternate spelling "bathychromic")...
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