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Testing and Spectrometric Characterization of Polymers
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
The following is a short description of some of the current techniques: Nuclear Overhauser effect. The nuclear Overhauser effect (NOE) only occurs between nuclei that share a dipole coupling, that is, their nuclei are so close that their magnetic dipoles interact. Techniques that use NOE enhance 13C spectra and allow spatial relationships of protons to be determined.Two-dimensional NMR. Basically, the two-dimensional NMR techniques of NOESY and COSY depend on the observation that spins on different protons interact with one another. Protons that are attached to adjacent atoms can be directly spin-coupled and thus can be studied using the COSY method. This technique allows the assignment of certain NMR frequencies by tracking from one atom to another. The NOESY approach is based on the observation that two protons closer than about 0.5 nm perturb each other's spins even if they are not closely coupled in the primary structure. This allows spatial geometry to be determined for certain molecules.
Nuclear Magnetic Resonance
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
The nuclear Overhauser effect (NOE) is a phenomenon that occurs from the transfer of nuclear spin polarization from one spin population to another via cross-relaxation. This magnetization transfer phenomenon was named after American physicist Albert Overhauser, who first proposed it in the early 1950s [40]. The phenomenon was demonstrated experimentally by T.R. Carver and C.P. Slichter in 1953 [41]. Although the Overhauser effect was first described in terms of polarization transfer between an electron and nuclear spins, the recognition that magnetization could also be transferred between nuclear spins caused the technique to become a dominant force in its application to three-dimensional structure elucidation [42].
Analytic Methods fo the Bioactive Compounds in Waste
Published in Quan V. Vuong, Utilisation of Bioactive Compounds from Agricultural and Food Waste, 2017
A Nuclear Overhauser Effect Spectroscopy (NOESY) homonuclear spectrum shows which signals in a 1H NMR are producing long range coupling through space, known as the Nuclear Overhauser Effect (NOE). The spectrum looks similar to a COSY spectrum, but the presence of a contour at the intersection of two signals symbolises coupling through space, instead of coupling through bonds as shown in the COSY spectrum (Williams and Fleming 1995).
Molecular scale insights from NMR studies of hybrid systems formed via doping silver QDs in 6CHBT liquid crystal: a quantitative investigation of their optoelectronic properties
Published in Liquid Crystals, 2023
Archana Kumari Singh, Satya Pal Singh
2) H-atoms present in the molecules are affected by the proximity of other H atoms. This effect shows its existence in two ways as- The resonant frequency of the H-atom (which we are observing) split into the two resonant frequencies nearly equal to each other, by the influence of nearby H-atom. As this effect gets stronger, the separation between the two frequencies becomes wider. This effect depends on the H–H bonding and dies off as the number of bonds increases, i.e.– 2 bonds 3 bonds 4 bonds. It is also sensitive to the bond angles connecting two H–H atoms. Thus, we can gather information about the orientation of H or a group of H atoms connected to the H-atom by single bonds.An increase in the nuclear magnetic resonance (NMR) signal is detected when spin polarisation transfer occurs between two adjacent hydrogen (H) atoms. This transfer takes place via dipole–dipole interactions, which are often mediated by cross-relaxation processes. It is possible to induce spin polarisation and enhance the NMR signal of another adjacent H atom by applying a specific radio frequency to one H atom. This type of enhancement is called as Nuclear Overhauser Effect (NOE), which operates directly through the space between H atoms. As separation increases, this effect quickly dies off and this influence is not observed after separation Å. NMR investigations provide us with information about nearby atoms, groups of atoms, or functional groups attached to an atom. NMR spectroscopy offers detailed information on the presence of various nuclei within a molecule. It enables us to determine the types and relative numbers of nuclei present, as well as their chemical surroundings and interactions.