CIDEP Chemically Induced Polarization

Both CIDNP and ESR techniques were used to study the mechanism for the photoreduction of 4-cyano-l-nitrobenzene in 2-propanol5. Evidence was obtained for hydrogen abstractions by triplet excited nitrobenzene moieties and for the existence of ArNHO, Ai N( )211 and hydroxyl amines. Time-resolved ESR experiments have also been carried out to elucidate the initial process in the photochemical reduction of aromatic nitro compounds6. CIDEP (chemically induced dynamic electron polarization) effects were observed for nitrobenzene anion radicals in the presence of triethylamine and the triplet mechanism was confirmed. 

Appropriate modifications of the ESR spectrometer and generation of free radicals by flash photolysis allow time-resolved (TR) ESR spectroscopy [71]. Spectra observed under these conditions are remarkable for their signal directions and intensities. They may be enhanced as much as one hundredfold and may appear in absorption, emission, or in a combination of both modes. These spectra indicate the intermediacy of radicals with substantial deviations from equilibrium populations. Significantly, the splitting pattern characteristic for the spin density distribution of the intermediate remains unaffected thus, the CIDEP (chemically induced dynamic electron polarization) enhancement facilitates the detection of short-lived radicals at low concentrations. 

CIDEP chemically induced dynamic electron polarization... 

CIDEP (Chemically Induced Dynamic Electron Polarization) Non-Boltzmann electron spin state population produced in thermal or photochemical reactions, either from a combination of radical pairs (called radical-pair mechanism), or directly from the triplet state (called triplet mechanism), and detected by ESR spectroscope... 

This organometallic radical product could, however, be detected by irradiation in glassy frozen matrices [34]. The alkyl radicals, as very short-lived metal-free products, could be observed and analyzed by FT-ESR with respect to CIDEP (chemically induced dynamic electron polarization) effects [34]. 

Electron Spin Resonance. ESR and CIDEP (chemically induced electron spin polarization) studies have been reported for radicals derived from phthalazine and related diazanaphthalenes. ° ... 

CIDEP chemically induced dynamic electron polarization CIDNP chemically induced dynamic nuclear polarization e electron... 

CIDEP Chemical induced dynamie eleetron polarization... 

CIDEP = Chemically Induced Dynamic Electron Polarization. For a review see F. J. Adrian, in Chemically Induced Magnetic Polarization, edited by L T. Muus, P. W. Atkins, K. A. McLauchlan, and J. B. Pedersen (Reidel, Dordrecht, 1977), Chap. 5, pp. 77-105. 

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

Blattler C, Jent F and Paul H 1990 A novel radical-triplet pair mechanism for chemically induced electron polarization (CIDEP) of free radicals in solution Chem. Phys. Lett. 166 375-80... 

Time-resolved laser flash ESR spectroscopy generates radicals with nonequilibrium spin populations and causes spectra with unusual signal directions and intensities. The signals may show absorption, emission, or both and be enhanced as much as 100-fold. Deviations from Boltzmann intensities, first noted in 1963, are known as chemically induced dynamic electron polarization (CIDEP). Because the splitting pattern of the intermediate remains unaffected, the CIDEP enhancement facilitates the detection of short-lived radicals. A related technique, fluorescence detected magnetic resonance (FDMR) offers improved time resolution and its sensitivity exceeds that of ESR. The FDMR experiment probes short-lived radical ion pairs, which form reaction products in electronically excited states that decay radiatively. ... 

A related technique is called chemically induced dynamic electron polarization (CIDEP). For a review, see Hore Joslin McLauchlan Chem. Soc. Rev, 1979, 8, 29-61. 

The photochemistry of benzaldehyde (90% 13C=0), 519, deoxybenzoin (99%) 13C=0), 521, and / -chloro benzoin (99% 13C=0), 522, in cyclohexane-Dn solution has been studied633 by spectroscopic techniques, such as XH chemically induced dynamic nuclear634 or electron polarization635 (CIDNP/CIDEP) or dynamic nuclear polarization636 (DNP). In all these cases the formation of benzaldehyde-D with emissive 13C=0 polarization has been observed and the results rationalized by intermolecular hydrogen (deuterium) abstraction by the photoexcited ketones from the solvent molecules and by reactions of cage-escaped radicals (equations 303-308), Benzoin, 520, is formed also. 

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