Electronic effect signs

In solution, the TPFPB salt of the methyl-substituted vinyl cation 19 has only limited stability. Decomposition into unidentified products took place during several days. In contrast, the steric and electronic effects provided by the /-butyl substituent confer indefinite stability to the vinyl cation 20 in the absence of nucleophiles. That is, according to the NMR experiments, a solution of 20 TPFPB in benzene showed no sign of decomposition even after weeks at room temperature. With the carborane anion [CBnH6Br6] suitable crystals for... 

In electronics, a well-established procedure to make statements on the sign of the electronic carriers is establishing the appropriate junctions (cf. diodes). The transformability of the semiconductor experiments to ion conductors suffers from the fact that the situation in ion conductors is more related to the situation in relaxation type semiconductors than to lifetime semiconductors note that only the latter shows the typical significant electronic effects such as in diodes or transistors. Nonetheless setting up ionic diodes and ionic transistors may be a worthwhile task for the future. (One such attempt to find out the nature of the ionic carriers (Oj or Vq ) in PbO by diode effects, viz. by a contact to the vacancy conductive YSZ, has been reported in Ref.217)... 

In order to study the influence of electronic effects on the stability of binary and ternary Zintl phases within the rigid band model (Sect. C.VI) Fig. 16 shows AEba (j of LiTl and LiCd as a function of the valence electron concentration. The maxima of the density of states curves for the B2 and the B32 types of structures occur at different energy values (cf. Fig. 15), and therefore AEband as a function of cve is an oscillating curve. The reasons why the curve for LiTl changes its sign are discussed below. 

Meanwhile, in the outer regions of the star, nuclei may be subjected to intense streams of neutrons, which have been generated by the nuclear processes in the core. These neutrons are captured by the nuclei in collisions, and several additional neutrons may accumulate in a given nucleus. At some stage of neutron accumulation, the nucleus becomes so unstable that it spits out an electron— a sign that, in effect, a neutron has collapsed into a proton and a new, heavier element has been formed. Thus, the kingdom gradually extends beyond iron, and elements up to uranium (and perhaps beyond) are formed. 

Later Cammarata [399] presented eq. 64 (recalculated) which describes meta-substituents by their n and a values and para-substituents by a steric parameter However, the steric parameter has the wrong sign the positive value of its regression coefficient implicates that steric bulk increases biological activity, which cannot be true. In addition, it is difficult to understand how an electronic effect can only be obtained for the wc/a-substituents. 

Three main conclusions can be deduced from Fig. 15. One, the oxidation of all the monomers proceeds via the same mechanism as shown by their linear fit (with a slope of m = 0.80). The mechanism requires the removal of a tt electron from the aromatic thiophene unit. Two, the less electronegative the monomer, the more easily it will be oxidized as the substituent constant p has a positive sign. Three, substituents do not deviate significantly from a linear relationship, as can be directly observed from Fig. 15. Thus, the S term is not important. Therefore, the j8 substituents exert primarily an electronic effect, which is adequately described by the p a term in the Hammett-Taft equation. 

A simple procedure reported for the isolation of jack-bean a-D-mannosidase was based on affinity chromatography on agarose-immobilized benzidine. The influence of substituents on the hydrolysis of substituted phenyl a-D-mannopyranosides by a-D-mannosidase from Medicago sativa seeds has been investigated. As indicated by structure-activity relations, the electronic effect of the substituent has an influence on the rate of formation of the intermediate D-mannosyl-enzyme complex. This effect depends not only on the nature of the substituent, but also on its position meta or para) and on the temperature of the experiment. Hammett-type linear free energy relationships show that the reaction constant p changes its sign at ca. 27 °C. Substrates... 

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