E.s.r. spectroscopy

The electronic state of iron in some natural iron compounds determination by Mossbauer and E.S.R. spectroscopy. W. T. Oosterhuis, Struct. Bonding (Berlin), 1974,20, 59-99 (66). 

A pictorial representation of the Tg-S mixing process follows from Fig. 6. Just as in normal n.m.r. or e.s.r. spectroscopy, precession can be represented by a vector model. When placed in an external magnetic field the two unpaired electrons of the radical pair 1 and 2 will precess... 

In most cases CIDNP is substantially more sensitive in detecting products produced by way of radical-pair intermediates than e.s.r. spectroscopy is in detecting free radicals. No hard and fast general rules are possible, however. 

Radicals escaping from a radical pair become uncorrelated as approaches zero. In the free (doublet) state they are detectable by e.s.r. spectroscopy. However, just as polarization of nuclear spins can occur in the radical pair, so polarization of electron spins can be produced. Provided that electron spin-lattice relaxation and free radical scavenging processes do not make the lifetime of the polarized radicals too short. 

In the area of spectroscopy, the application, with computer assistance, of the theory to observed spectra should provide much readier access to magnetic resonance parameters (e.g., radical jr-factors, absolute signs of a- and J-values) than has been available hitherto. Moreover, for rtidical parameters, CIDNP is much more versatile than e.s.r. spectroscopy, since it can readily handle even very reactive radicals. 

A number of the techniques that have been employed have the ability to directly monitor free-radical species either in vitro or in vivo [predominantly those involving electron spin resonance (e.s.r.) spectroscopy]. However, since many physiologically relevant free radicals have extremely short half-lives (e.g. 10 s for OH), the majority of the methods utilized detect products arising from their reactions with chemical components present (i.e. indirect methods). These indirect methods for... 

Despite their short half-lives, it is possible to detect free radicals in biological tissues by the addition of nonradicals such as nitrones or nitroso compounds, which act as spin traps by forming relatively stable free radicals on reaction with the endogenous radical species. Utilizing the technique of electron spin resonance (e.s.r.) spectroscopy, we have demonstrated ROM generation by human rheumatoid synovium when subjected to cycles of hypoxia/normoxia in vitro. Using 3,5-dibromo-4-nitroso-benzenesulphonate (DBNBS) as a spin trap, a... 

The formation of appreciable quantities (up to "oQ0% based on the initial additive concentration) of the grafted substituted hydroxylamine O W0PP as from reaction 7) in photo-degrading PPH can be demonstrated by indirect methods (10, 11). For example after the rapid loss of the initial concentration of a piperidine or its nitroxide in PPH film, heating the film immersed in isooctane for several hours at 100 C in the presence of oxygen causes the re-appearance of nitroxide in appreciable quantities as measured by e.s.r. spectroscopy (ll). This nitroxide most likely results from a reaction analogous to reaction 8 (l2). In addition we have observed the ) N-0-C band (at 1306 cm 1) in the infrared spectrum of irradiated, nitroxide-containing PP films by Fourier Transform IR spectroscopy (ll)., ... 

F. Gerson, High Resolution E.S.R. Spectroscopy, John Wiley and Sons Ltd., London, 1970. 

The effect of ionizing radiation on molecular or ionic solids is to eject electrons, which often subsequently react at sites in the material well removed from the residual electron-loss centre. These electron-loss and electron-gain centres, or breakdown products thereof, are paramagnetic and have been extensively studied by e.s.r. spectroscopy. Results for a wide range of organo metals both as pure compounds and as dilute solid solutions are used to illustrate this action. Aspects of the electronic structures of these centres are derived from the spectra and aspects of redox mechanisms are discussed. 

Some examples of specific electron-capture by various organo-metallic compounds in such solvents are summarised in reactions [5]-[10] [refs. (5)-(H)) respectively]. In some cases, the parent anion ( AB ) is detected by e.s.r. spectroscopy, but in others subsequent reactions have occurred. 

Group VIIA (Mn, Tc. Re). A number of mononuclear manganese carbonyl derivatives have been y- irradiated and examined by e.s.r. spectroscopy. The motivation behind much of this effort was the search for the elusive radical Mn(CO)s. The e.s.r. spectrum of this species is now firmly (35-37) established (Figure 4), although there is still some suggestion that the true "naked Mn(CO)s has yet to be observed (37). 

We conclude that for organometallic derivatives, radiolysis can be used as an excellent method for inducing specific electron-loss or electron-addition. Furthermore, this can be done at very low temperatures such that, often, the primary gain and loss species are formed and can be characterised by e.s.r. spectroscopy. Thus this technique is a useful complement to more conventional studies of redox reactions. 

The anion of di-isopropyl phosphorothiolothionic acid (26) reduces hydroxyl radicals, and the radical (27) so produced is detectable by e.s.r.33 Attempts to observe these radicals by photolysis of the free acid were unsuccessful. However, the use of a spin trap (e.g. TV-methylene-t-butylamine iV-oxide) enabled radicals in this system and other closely related systems [e.g. with (28)] to be observed by e.s.r. spectroscopy. 

The Raman spectrum of VCI4 has been reported and values for the force constants and various thermodynamic parameters of the molecules have been calculated. VCI4 has been used to investigate the structure of oxide surfaces. The number of OH groups per unit area follows from the amount of HCl liberated, and the arrangement of such groups can then be determined by e.s.r. spectroscopy. ... 

Other Compounds. Adsorption of MeNC into a cobalt(ii) zeolite at — 196"C was followed by e.s.r. spectroscopy, and the presence of low-spin [Co-(CNMe)j] and [Co(CNMe) ] complex cations demonstrated.This work represents one of the few successful attempts to produce well-characterized transition-metal complexes in a zeolite framework. Addition of NaCp to CoClj and [(BgC2H,Q)CoCp], previously reduced with sodium naphthalide gives a new bimetallic complex, for which structure (94) is proposed. ... 

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