Chemically induced nuclear polarization

Chemically Induced Nuclear Polarization (CIDNP)-Experiments... 

In solution, the triplet biradical 14b dimerizes, and the dimeric products are formed with strong chemically induced nuclear polarization. The absolute rate of the dimerization at 146 K, as monitored in viscous solution by ESR spectroscopy, is just about that predicted by the spin-corrected encounter frequency under those conditions. The cycloaddition of the triplet with a typical alkene, acrylonitrile, also can be followed in this way. 

Finally, recall that geminate processes are detected by the spectroscopic technique of chemically induced nuclear polarization. Because the CIDNP spectrum is directly related to properties of the caged radical pair, as explained in the Appendix to this chapter, much useful information about the nature of caged radicals and their fate can be obtained by this method. 

The seminal work of Marcus and Hush has had a significant impact on the development of PET. Pioneering efforts by Sutin, Hopfield, Jortner, and others established the connection between thermal electron transfer and photoelectron transfer [6]. This work set the stage for a notable series of experiments where laser flash spectroscopy [7], chemically induced nuclear polarization [8], resonance Raman spectroscopy [9], time-resolved microwave conductivity [10], and time-resolved photoacoustic calorimetry [11], to site only a few examples, have been successfully employed to chart the dynamics of PET in homogeneous solution, the solid-state, and organized assemblies. 

Chemically induced nuclear polarizations have been observed in solutions of reacting organo-metallic substances and in solutions of peroxides and azo compounds undergoing thermal decomposition. Since the chemically induced nuclear polarization depends on the lifetimes of the radicals formed and on the relaxation times of the nuclei, observation of such effects can lead to information about which radicals are formed and their lifetime. 

B1.16 Chemically-induced nuclear and electron polarization (CIDNP and CIDEP)... 

Closs G L and Trifunac A D 1969 Chemically Induced nuclear spin polarization as a tool for determination of spin multiplicities of radical-pair precursors J. Am. Chem. Soc. 91 4554-5... 

The first example of chemically induced multiplet polarization was observed on treatment of a solution of n-butyl bromide and n-butyl lithium in hexane with a little ether to initiate reaction by depolymerizing the organometallic compound (Ward and Lawler, 1967). Polarization (E/A) of the protons on carbon atoms 1 and 2 in the 1-butene produced was observed and taken as evidence of the correctness of an earlier suggestion (Bryce-Smith, 1956) that radical intermediates are involved in this elimination. Similar observations were made in the reaction of t-butyl lithium with n-butyl bromide when both 1-butene and isobutene were found to be polarized. The observations were particularly significant because multiplet polarization could not be explained by the electron-nuclear cross-relaxation theory of CIDNP then being advanced to explain net polarization (Lawler, 1967 Bargon and Fischer, 1967). 

The technique most recently introduced to study radical cations is chemically induced dynamic polarization (CIDNP), a nuclear resonance method based on the observation of transient signals, substantially enhanced in either absorption or emission. These effects are induced as a result of magnetic interactions in radical or radical ion pairs on the nanosecond timescale. This method requires acquisition of an NMR spectrum during (or within a few seconds of) the generation of the radical ion pairs. The CIDNP technique is applied in solution, typically at room... 

ESR spectroscopy has found wide-spread use for the detection of radical intermediates in electrode processes 40 For the same purpose, the newly developed technique of trapping short-lived radicals by nitrones or nitroso compounds 40d-> should be of considerable interest, as should also the chemically induced nuclear spin polarization (CINP) phenomenon 40e-1 be. 

The current theories of chemically induced magnetic polarization can therefore be summarized into the two basically different mechanisms the photoexcited triplet mechanism (PTM) responsible for the initial electron polarization and the observed Overhauser effect in nuclear polarization, and the radical-pair mechanism which, to date, accounts for almost the remaining bulk of the known polarization systems. We proceed to describe the simple physical models of these two mechanisms by beginning with the more sophisticated radical-pair theory. 

Garst, J. F., Cox, R. H. Wurtz reaction. Chemically induced nuclear spin polarization in reactions of alkyl iodides with sodium mirrors. J. Am. Chem. Soc. 1970, 92, 6389-6391. 

Chemically-induced spin polarization was one of the last truly new physical phenomena in chemistry to be discovered and explained during this century. So unusual were the observations and so ground-breaking the theoretical descriptions that, over a very short time period, the chemist s way of thinking about free radical reactions and how to study them was fundamentally changed. After the earliest experimental reports of unusual phases of electron paramagnetic resonance (EPR) (1963) [1] and nuclear magnetic resonance (NMR)... 

Roth, H.D., Reaction of methylene in solutions. Selective abstraction reactions of CHj and CHj, /. Am. Chem. Soc., 93, 4935, 1971 Roth, H.D., Chemically induced nuclear spin polarization in the study of carbene reaction mechanisms, Acc. Chem. Res., 10, 85,1977. 

Kaptein R and Oosterhoff J L 1969 Chemically Induced dynamic nuclear polarization III (anomalous multiplets of radical coupling and disproportionation products) Chem. Phys. Lett. 4 214-16... 

Goez M 1995 An introduction to chemically induced dynamic nuclear polarization Concepts Magn. Reson. 7 69-86... 

Kaptein R 1971 Simple rules for chemically induced dynamic nuclear polarization J. Chem. See. Chem. Commun. 732-3... 

Morozova O B, Tsentalovich Y P, Yurkovskaya A V and Sagdeev R Z 1998 Consecutive biradicals during the photolysis of 2,12-dihydroxy-2,12-dimethylcyclododecanone low- and high-field chemically induced dynamic nuclear polarizations (CIDNP) study J. Rhys. Chem. A 102 3492-7... 

Carboxamides, formation from ArNj 243 2-Carboxybenzenediazonium zwitterion, see 2-Diazoniobenzenecarboxylate Carboxy-de-diazoniation 241 f. Carcinogenicity 319 Chemically induced dynamic nuclear polarization, see CIDNP Chloro-de-diazoniation 194, 230ff., 247, 270, 277... 

CIDNP chemically induced dynamic nuclear polarization... 

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... 

Kaptein, R. (1971b). Chemically Induced Dynamic Nuclear Polarization , Thesis, Leiden. 

Chemically Induced Dynamic Nuclear Polarization Complete Neglect of Differential Overlap cyclopentadienyl diethyl azodicarboxylate... 

Observation of spin-polarized products resulting from these radical pairs by the method of chemically induced dynamic nuclear polarization (CIDNP)<67) was accomplished by photolysis in the probe of an NMR spectrometer using perfluoromethylcyclohexane as solvent. The results obtained were consistent with nuclear spin polarization steps involving radical pairs formed from dissociated radicals and also directly from excited states, although the former could not be detected in carbon tetrachloride, probably due to radical scavenging by the solvent. It was not possible to determine the fraction of the reaction proceeding by singlet and triplet radical pairs.<68)... 

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... 

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