Chemically induced dynamic nuclear applications

CHEMICALLY INDUCED DYNAMIC NUCLEAR SPIN POLARIZATION AND ITS APPLICATIONS... 

The first reports of the observation of transient emission and enhanced absorption signals in the H-n.m.r. spectra of solutions in which radical reactions were taking place appeared in 1967. The importance of the phenomenon, named Chemically Induced Dynamic Nuclear Spin Polarization (CIDNP), in radical chemistry was quickly recognized. Since that time, an explosive growth in the number of publications on the subject has occurred and CIDNP has been detected in H, C, N, and P as well as H-n.m.r. spectra. Nevertheless, the number of groups engaged in research in this area is comparatively small. This may be a consequence of the apparent complexity of the subject. It is the purpose of this review to describe in a quahtative way the origin of CIDNP and to survey the published applications of the phenomenon in... 

Chain processes, free radical, in aliphatic systems involving an electron transfer reaction, 23,271 Charge density-NMR chemical shift correlation in organic ions, 11,125 Chemically induced dynamic nuclear spin polarization and its applications, 10, 53 Chemiluminescence of organic compounds, 18,187... 

Chemically induced dynamic nuclear spin polarization and its applications, 10, 53... 

Among NMR methods providing insight into radical ions, chemically induced dynamic nuclear polarization (CIDNP) has proved especially useful it results in enhanced transient signals, in absorption or emission CIDNP effects were first reported in 1967 their application was soon extended to radical ions. The method lends itself to modest time resolution. 

H. R. Ward, "Chemically Induced Dynamic Nuclear Polarization (CIDNP). I. The Phenomenon, Examples, and Applications, Accfs. Chem. Res. 5, 18 (1972). 

Nuclear magnetic resonance has proved to be an invaluable technique for many applications and it has been used prominently in the characterization of organic radical ions. We mention three areas of application in this context selective chemical shift differences differential line broadening and chemically induced dynamic nuclear polarization. Each of these methods has provided insights into the structures and reactivities of numerous radical ions. 

Whereas NMR spectroscopy is generally applied to the diamagnetic allyl, pentadienyl, or cyclopentadienyl cations or anions, this technique is generally not applicable to the analogous radical species, although CIDNP (chemically induced dynamic nuclear polarization) has been observed for allyl140 and pentadienyl radical species139. More useful for the radicals, naturally, is EPR spectroscopy. 

Finally, it should be pointed out that methods used to study short-lived chemical intermediates in fast thermal reactions may be applicable also to photochemical studies. Radical intermediates, however generated, can be studied by CIDNP (chemically induced dynamic nuclear spin polarization), in which the n.m.r. spectrum of the reaction mixture is recorded during the reaction period. If a substrate is continuously irradiated with ultraviolet/visible light in the cavity of an n.m.r. spectrometer, the resulting n.m.r. spectrum ot the substrale/product mixture exhibits intensity variations as compared with the normal spectrum—intensity enhancement, reduction or even reversal (i.e. emission). Note that the spectrum involved is not... 

The first discovery of chemically induced dynamic electron polarization (CIDEP) was made by Fessenden and Schuler in 1963 (58). These authors observed the abnormal spectra of the H atoms produced during the irradiation of liquid methane. The low-field line in the esr spectrum was inverted compared to the corresponding high-field line. The related chemically induced dynamic nuclear polarization effect (CIDNP) was reported independently four years later by Bargon et al. (22) and by Ward and Lawler (134). Because of the wider application of nmr in chemistry, the CIDNP effect immediately attracted considerable theoretical and experimental attention, and an elegant theory based on a radical-pair model (RPM) was advanced to explain the effect. The remarkable development of the radical-pair theory has obviously brought cross-fertilization to the then-lesser-known CIDEP phenomenon. 

Porter N A, Marnett L J, Lochmuller C H, Closs G L and Shobtaki M 1972 Application of chemically induced dynamic nuclear polarization to a study of the decomposition of unsymmetric azo compounds J. 

Chemically Induced Dynamic Nuclear Polarization (CIDNP) This term has been used to describe the enhancement of nuclear spin polarization observed In the NMR spectra of compounds undergoing radical reactions. Some exciting applications are described In Chapter X. 

There are a variety of techniques for the determination of the various parameters of the spin-Hamiltonian. Often applied are Electron Paramagnetic or Spin Resonance (EPR, ESR), Electron Nuclear Double Resonance (ENDOR), Electron Electron Double Resonance (ELDOR), Nuclear Magnetic Resonance (NMR), occassionally utilizing effects of Chemically Induced Dynamic Nuclear Polarization (CIDNP), Optical Detection of Magnetic Resonance (ODMR), Atomic Beam Spectroscopy and Optical Spectroscopy. The extraction of the magnetic parameters from the spectra obtained by application of these and related techniques follows procedures which may in detail depend on the technique, the state of the sample (gaseous, liquid, unordered solid, ordered solid) and on spectral resolution. For particulars, the reader is referred to the general references (D). 

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