Electrical induction effects

In a d.c. system the current distribution through the cross-section of a current-canying conductor is uniform as it consists of only the resistance. In an a.c. system the inductive effect caused by the induced-electric field causes skin and proximity effects. These effects play a complex role in determining the current distribution through the cross-section of a conductor. In an a.c. system, the inductance of a conductor varies with the depth of the conductor due to the skin effect. This inductance is further affected by the presence of another current-carrying conductor in the vicinity (the proximity effect). Thus, the impedance and the current distribution (density) through the cross-section of the conductor vaiy. Both these factors on an a.c. system tend to increase the effective... 

A cLirrent-earrying conducior produces an electric field around it which induces a back e.m.f. and causes an inductive effect. This e.m.f. is produced in the conductor hy its own electric field cutting the conductor. It is more dense at the centre and becomes less at the surface. The conducior thus has a higher inductance al the centre than at the surface, and causes an uneven distribution of current... 

Alternating-current motors are classified as induction motors or synchronous motors. Faraday found that a stationaiy wire in a magnetic field produced no current. However, when the wire continues to move across magnetic lines of force, it produces a continual current. When the motion stops, so does the current. Thus Faraday proved that electric current is only produced from relative motion between the wire and magnetic field. It is called an induced current—an electromagnetic induction effect. 

The magnitude of the electrical effect is comparable to that of the trans-heterovinylene sets. The difference in magnitude between the a values for the syn and anti phenyl ketoximes is significant and suggests that the inductive effect alone cannot account for the observed substituent effect. If the inductive effect were operating by itself, the a values for syn and anti sets would be the same. 

The discussion above has been more or less empirical and descriptive. However, considerable effort has been made to interpret 3-SCS on a more physical basis. Electric-field effects (71-75) were invoked to explain signal shifts of 3-carbon atoms induced by protonation of amines (157,158) (cf. Section II-B-3). This approach was later extended to other functionalities by Schneider and coworkers, who assumed that the SEF component (E2) rather than inductive properties of the substituents should be responsible for 3-SCS (113). They found fairly linear correlations of 3-SCS(X ) and 3-SCS(X ) in cyclohexyl derivatives (76) and attributed the difference between these for a given X to a widening of the C -Cp-Cv bond angle by 2.2° in the axial conformer (114,159). The decrease of 3-SCS in the order primary Cp —> secondary Cp — tertiary Cp — quaternary Cp was explained by electron-charge polarization in the Cp-C" bond(s) induced by the LEF component of the C -X dipole, which is already of significance at this distance, though ( 2) still dominates (160). Such an electron flow toward the 3 carbon is expected to be much more pronounced in C-C than in C-H bonds because of the polarizability difference (aCH = 0.79 acc = 1.12) (150,151,160). 

When the conditions under which the reactivity or property that is measured are held constant and L is chosen as the measure of the extent of electrical-effect transmission, the classical inductive effect is given by equation 24 ... 

Quantum chemical calculations on substituted alkanes are in agreement with a through-space (field) transmission of substituent electrical effects . In view of the ever-increasing evidence for through-space transmission of electrical effects, it is time to make a conclusive statement. There is no inductive-effect component in electrical-effect transmission ... 

Besides the direct electrical induction of electro-optical effects in liquid crystals, their activation by illumination of photoconductors could be of great technical interest. This method might well permit the electro-optical properties of nematic liquid crystals to be used on a larger scale, because photoconductor activation may eventually be applied to light amplification, optical data processing, and projection display systems, or used for recording phase-type holograms. 

Inductive and electric field effects of the substituents may overlap the o-mesomeric effects. However, the m and p shifts of monosubstituted benzenes generally follow the pattern discussed above. 

In aromatic compounds carbon-13 shifts are largely determined by mesomeric (resonance) and inductive effects. Field effects arising from through-space polarization of the n system by the electric field of a substituent, and the influences of steric (y) effects on the ortho carbon nuclei should also be considered. Substituted carbon (C-l) shifts are further influenced by the anisotropy effect of triple bonds (alkynyl and cyano groups) and by heavy atom shielding. 

It can be seen from Table 4.78 that the a increments can be reasonably rationalized in terms of inductive effects (Pauling electronegativities), while the shielding of carbons y to the substituent is generally attributed to a steric polarization of the yC — H bond. Inductive and electric field effects contribute to the f) increments. As electric fields can be evaluated only in rare cases, no general trend for the [) effect has been recognized so far. Frequently, the a and increments depend on whether a substituent X is terminal (n) or central (iso). If available, the iso increments are also given in Table 4.78. 

The second TT-inductive effect is the field effect, tt which arises through polarization of the whole 7r-system due to the electric dipole of (CH2) Y, as shown in 1. 

Romson JL, Haack DW, Lucchesi BR (1980b) Electrical induction of coronary artery thrombosis in the ambulatory canine a model for in vivo evaluation of anti-thrombotic agents. Thromb Res 17 841-853 Ruebsamen K, Kirchengast M (1998) Thrombin inhibition and intracoronary thrombus formation effect of polyethylene glycol-coupled hirudin in the stenosed, locally injured canine coronary artery. Coron Artery Dis 9 35-42 Sullivan J, Hansen P, Rahko PS, Folts JD (1992) Continous measurement of left ventricular performance during and after maximal isometric deadlift exercise. Circulation 85 1406-1413... 

Here E, D, and P represent, respectively, the electric field, electric induction (or displacement), and electric polarization vectors P (D - )/4x. The integration must be carried out over all space penetrated by the electrostatic field. Equation (5.6.1), while correct, is awkward in several respects. First, there is the need to integrate over all space, including the region outside the system of interest. In the presence of a medium, the electric lines of force not only are present within the specimen, but also bulge out in all directions away from the system these effects must be included in (5.6.1). Second, there is a tendency in the literature to associate the first term in (5.6.1b) with the establishment of the electric field in free space, and the second term with the reaction of the medium to the electric field. This is wrong The quantity D is subject to direct experimental control because it is linked by Maxwell s equation to the presence of free charges by contrast, E is in part a reaction field that also includes the... 

It has long been known that a substituent X in an XGY system can exert an electrical effect on an active site Y. It is also well known that the electrical effect which results when X is bonded to an sp hybridized carbon atom differs from that observed when X is bonded to an sp or an sp hybridized carbon atom. As electron delocalization is minimal, in the first case, it has been chosen as the reference system. The electrical effect observed in systems of this type is a universal electrical effect which occurs in all systems. In the second type of system, a second effect (resonance effect) occurs due to delocalization, which is dependent both on the inherent capacity for delocalization and on the electronic demand of file active site. In systems of the second type the overall (total) electrical effect is assumed to be a combination of the universal and the delocalized electrical effects. For many years an argument has sometimes raged (and at other times whimpered) concerning the mode of transmission of the universal electrical effect. Two models were proposed originally by Derick, a through bond model (the inductive effect) and a through space model (the field effect). These proposals were developed into the classical inductive effect (CIE) and the classical field effect (CFE)" models. As the CIE model could not account... 

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