Electronic polarization

More P J 1989 Analysis of polarized electron paramagnetic resonance spectra Advanced EPR Applications In Biology and Biochemistry ed A J Hoff (Amsterdam Elsevier) ch 12... 

Closs G L, Forbes M D E and Norris J R 1987 Spin-polarized electron paramagnetic resonance spectra of radical pairs in micelles. Observation of electron spin-spin interactions J. Phys. Chem. 91 3592-9... 

The dielectric constant is a measure of the ease with which charged species in a material can be displaced to form dipoles. There are four primary mechanisms of polarization in glasses (13) electronic, atomic, orientational, and interfacial polarization. Electronic polarization arises from the displacement of electron clouds and is important at optical (ultraviolet) frequencies. At optical frequencies, the dielectric constant of a glass is related to the refractive index k =. Atomic polarization occurs at infrared frequencies and involves the displacement of positive and negative ions. 

The high reactivity of the acyl chlorides also reflects the polar electron-withdrawing effect of the chlorine, which more than outweighs the small 7t-donor effect. 

Research on the nature of substituent constants continues, with results that can bewilder the nonspecialist. The dominant approach is a statistical one, and the main goal is to dissect substituent effects into separate electronic causes. This has led to a proliferation of terms, symbols, and conclusions. A central issue is (here we change terminology somewhat from our earlier usage) to determine the balance of field and inductive effects contributing to the observed polar electronic effect. In... 

The symbol k or K is the rate or equilibrium constant, respectively, for a side-chain reaction of a meta- or para-substituted benzene derivative, and k° or K° denotes the statistical quantity (intercept term) approximating to k or K for the parent or unsubstituted compound. The substituent constant a measures the polar (electronic) effect of replacing H by a given substituent (in the meta- or para-position) and is, in principle, independent of the nature of the reaction. The reaction constant p depends on the nature of... 

On this basis, it might well be expected that the p value, of otherwise similar reactions, would decrease as the reaction centre is moved further away from the substituents that are exerting a polar, electronic effect upon it. This is borne out by the p values for the aqueous ionisation of the acids (13)—(16) ... 

Two substituents however, the powerfully electron-withdrawing p-NOz and p-CN, lie above this straight line indicating that p-N02 phenol and p-CN phenol are in fact stronger acids than we might have expected them to be. Why this is so becomes apparent if we write out the structures of the species involved in both ionisation equilibria for, say, the p-NOz compounds (18 and 19) and examine the polar, electronic effects that can operate in them ... 

Ray K, Ananthavel SP, Waldeck DH, Naaman R (1999) Asymmetric scattering of polarized electrons by organized organic films of chiral molecules. Science 283(5403) 814—816... 

More than forty years ago, Lee and Yang [8] observed anomalies in the decay patterns of theta and tau mesons, which suggested to them that parity was not conserved for certain weak interactions involved in the (3-decay of radioactive nuclei. This Nobel-prize-winning prediction was experimentally validated by Wu et al., [9] who found that the longitudinally polarized electrons emitted during the (3-decay of Co nuclei had a notable (40%) left-handed bias, i.e., their spins were predominantly antiparallel to their directions of motion. These experiments established that parity violation and symmetry breaking occurred at the nuclear level. 

For recent reviews, see Binder, K.,in Phase Transitions and Critical Phenomena, Vol. 8 (Ed. C. Domb and J. L. Lebowitz), Academic, New York, 1983 H. W. Diehl ibid., Vol. 1, Academic, New York 19 Binder, K., in Polarized Electrons from Surfaces (Ed. R. Feder), World Scientific, Singapore, 1985. 

Spin Polarized Electron Tunneling and Magnetoresistance in Molecular Junctions... 

Meservey R, Tedrow PM (1994) Spin-polarized electron tunneling. Phys Rep 238 173-243... 

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