Hyper fine splitting

Poly (4-methyl-1-pentene). Poly(4-methyl-l-pentene) has not yet drawn much attention in radiation chemistry. As far as we know, only one study on high energy-irradiated poly(4-methyl-l-pentene) has been published (25), and this was in the form of a short communication. The ESR spectrum at liquid nitrogen temperature was a sextet with a hyper-fine splitting constant of 23 gauss. The radicals producing this spectrum were supposed to have structure XXI—i.e., radicals formed by side-chain scission. 

The ESR spectrum of radicals in poly(4-methyl-l-pentene) induced by ultraviolet light 4,5) is composed of a sharp quartet with the hyper-fine splitting constant of 22.5 gauss and a broad quartet. The sharp component has been attributed to methyl radicals (XI) while the broad component could be caused by polymer radicals of structures XXIII and/or XXIV. 

As stated in the previous section, reduction of thieno[3,2-6]thiophene (2) with Na-K alloy at —100° results in the formation of a radical-anion.187,18 With AlClj in nitromethane at —20°, or SbCl, in methylene chloride at —60°, a radical-cation was obtained.237 The experimental hyper fine splitting constants (HFSC) data are shown in Eq. (73). 

Fig. 5. Comparison of (former and recent) calculations for the electromagnetic hyper-fine splittings. The calculations include vacuum polarization ABvp, electromagnetic fine Z Bfs and hyperfine structure ABhfs...

For the benzosemiquinone radical anion, one has nine tt electrons, with two each in the fonr lowest levels and the nnpaired electron residing in 5. Using the HMO resnlts in the tables, calcnlate p for the carbons attached to the protons and compare with the valnes obtained from your experimental results and the McConnell relation [Eq. (9)] with Q = -22.5 ganss. Note that the calculations provide a basis for assignment of the hyper-fine splitting constants to specific ring protons in orfAo-benzosemiqninone. Draw out the possible valence-bond resonance structures for both ortho and para compounds and dis-cnss the relative importance of these. 

The simplest monocyclic thiophene cation-radicals which are persistent at ambient temperature and for which ESR spectra have been recorded and assigned are a series of 2,5-bis(alkylthio)thiophene cation-radicals. These radicals exhibit conformational isomerism. Thus, 2,5-bis(metliyltliio)-tliiophene cation-radicals exists as a mixture of 75% of the symmetrical S-cis-cis isomer (93A) and 25% of the unsymmetrical S-cis-trans isomer (93B) with no detectable concentration of the symmetrical S-trans-trans isomer. The radicals were formed by treatment of the parent heterocycles in nitro-methane with AICI3 the assignments were made on the basis of both S- and C-alkyl substitution experiments and supported by MO calculations (hyper-fine splittings given for 93A and B are in gauss). 

II, B,3,a and 3) Japanese workers observed ESR spectra of 194 when selenoxanthylium salts were treated with organometallic reagents however, their conclusions drawn in this work have been refuted. Hyper-fine splittings for 194 are indicated in gauss. 

The spectrum from cis-polyisoprene tensile tested in (nominally) oxygen free nitrogen, shown in Fig. 32, is a six line spectrum with approximately 12 G hyper-fine splitting. Polymer radicals are centred around the free spin -value (g-= 2) and structure in the spectrum is invariably due to nuclear hyperfine structure. The peroxy... 

Figure 11). The g-values and hyper-fine splitting constants for samples prepared via either route showed full agreement, hence the authors concluded that also the... 

From the ENDOR spectriun with these two lines, one can derive both the hyper-fine splitting constant. A, and the nuclear factor, gi (characteristic of given nucleus) with high accuracy. 

Fig. 4.17.1. Correlation of the carbonyl oxygen and carbon hyper-fine splitting constants (in gauss) of p-benzosemiquinone with the Z value of the solvent O = O =...

Another EPR signal, at gL = 1.999 and g = 1.927, with resolved " N hyper-fine splitting, is observed for an intermediate Fe NO" complex during the reduction of nitroprusside by thiols [58]. Reaction of nitropmsside with a thiol such as cysteine leads to a one-electron reduction of the complex and formation of... 

The combination of laser-spectroscopic techniques with molecular beams and RF spectroscopy has considerably enlarged the application range of optical-RF double-resonance schemes. This optical-RF double-resonance method has now become a very powerful technique for high-precision measurements of electric or magnetic dipole moments, of Lande factors, and of fine or hyper-fine splitting in atoms and molecules. It is therefore used in many laboratories. 

More than twenty years ago, in Kivelson s famous paper a relation between hyper-fine splitting due to nitrogen nuclei and correlation time of the motion of molecules containing a nitroxide radical was proposed. A few years later, stable free radicals containing nitroxide radicals, such as ... 

Consider the ethyl radical as an example (Fig. 4). Since its 2p-orbital has a node at the nucleus, no contact interaction is likely to take place in this organic free radical. However, the spin exchange interaction of the unpaired electron of the 2p-orbital with the electrons of the spin density at the nucleus. Furthermore, this interaction causes the electron spins to polarize at each a-proton and leads to a hyperfine structure. Accordingly, the hyper-fine splitting constant a for the a-proton is proportional to the unpaired electron density at the radical center. Thus we obtain the relation... 

Finally, the third broadening mechanism is hyper-fine splitting which is caused by isotope shifts and nuclear spin splitting. Generally a spectral line consists of n hyperfine components with relative intensities, bj, (Z, Li bj = 1) that are located at a distance Ao),-from the component with the minimum frequency. Each component is Doppler and collision broadened and described by the Voigt function [6]. Thus in the general case the emission /( ) and absorption k((0) profiles are presented as follows ... 

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