Axial viewing geometry

Figure 28-8 Viewing geometries for ICP sources, (a) Radial geometry used in ICP atomic emission spectrometers (b) axial geometry used in ICP mass spectrometers and in several ICP atomic emission spectrometers.

Mechanisms for such reactions have been viewed by the effective coordination number of the transition state. Bond rupture processes proceed via five-coordinate transition states for which idealized square-pyramidal (SP) and trigonal-bipyramidal (TBP) geometries with the dangling ligand axial or equatorial have been considered. Twist mechanisms are considered to proceed via six-coordinate transition states with idealized trigonal prismatic (TP) geometry. Twists of the chelate rings about the real or pseudo C3 axis in the case of the cis or trans isomer, respectively, and about the... 

Analgesics of the 4-arylpiperidine class mimic the geometry of a large portion of morphine when in the axial phenyl chair conformation 33a and were thus earlier believed capable of accommodation at the proposed receptor. This view later fell into disrepute as a result of conformational considerations and particularly the radically different structure-activity relationships in regard to N-substituents and the influence of phenolic hydroxyl between the 4-arylpiperidine and morphine groups. There is evidence that reversed esters of pethidine and other 4-phenylpiperidines with C-4 oxygen functions bind in the equatorial 4-phenyl chair conformation 33b, and receptor modifications necessary to allow uptake of both ax and eq 4-phenyl chairs are discussed... 

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