Electron spin resonance solid-state reactions

Short-lived organic radicals, electron spin resonance studies of, 5, 53 Small-ring hydrocarbons, gas-phase pyrolysis of, 4, 147 Solid state, tautomerism in the, 32, 129 Solid-state chemistry, topochemical phenomena in, 15, 63 Solids, organic, electrical conduction in, 16, 159 Solutions, reactions in, entropies of activation and mechanisms, 1, 1 Solvation and protonation in strong aqueous acids, 13, 83 Solvent effects, reaction coordinates, and reorganization energies on nucleophilic substitution reactions in aqueous solution, 38, 161 Solvent, protic and dipolar aprotic, rates of bimolecular substitution-reactions in,... 

Nishimoto S, Hatta H, Ueshima H, Kagiya T (1992) 1-(5 -Fluoro-6 -hydroxy-5, 6 -dihydrouracil-5 -yl)-5-fluorouracil,a novel N(1)-C(5) linked dimer that releases 5-fluorouracil by radiation activation under hypoxic conditions. J Med Chem 35 2711-2712 Norman ROC, Storey PM, West PR (1970) Electron spin resonance studies, part XXV. Reactions of the sulphate radical anion with organic compounds. J Chem Soc (B) 1087-1095 Novais HM, Steenken S (1986) ESR studies of electron and hydrogen adducts of thymine and uracil and their derivatives and of 4,6-dihydroxypyrimidines in aqueous solution. Comparison with data from solid state. The protonation at carbon of the electron adducts. J Am Chem Soc 108 1-6... 

Electron spin resonance (ESR) spectroscopy is of application to organic species containing unpaired electrons radicals, radical ions and triplet states, and is much more sensitive than NMR it is an extremely powerful tool in the field of radical chemistry (see Chapter 10). Highly unstable radicals can be generated in situ or, if necessary, trapped into solid matrices at very low temperatures. Examples of the application of this techniques include study of the formation of radical cations of methoxylated benzenes by reaction with different strong oxidants in aqueous solution [45], and the study of the photodissociation of N-trityl-anilines [46],... 

Possible electron transfer processes merit discussion, a priori, because of the relatively low solid-state ionization energy of the PDA backbone (2) and the strong acceptor character of bromine. Since the resultant products of bromination are largely diamagnetic, a long-lived electron transfer product is not involved. Moreover, when the bromination reaction is monitored by electron-spin resonance ( ), no buildup of a paramagnetic species was noted. In view of these observations, reaction via electron transfer as a major process is ruled out. 

At room tenqrerature, the life-time of the transient species is generally very small. However, in the solid state at sufficiently low tenqrerature (77 K) tte reaction of transients can be slowed down so much that they can be obsmed over poiods of minutes or hours and could be conveniently studied tty optical absorption investigations in glassy matrix of 3-meth )entane (3MP), 2-metityhetrahydrofiiran and by electron spin resonance measurements [44-50]. With the availability of pulse ladiolysis technique, the idoitity of transients can be investigated at room temperature [29-39]. 

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