Cationic structure related

Cations structurally related to benzhydryl are anthracenyl (7)75 87 and fluorenyl (8).69 There has been some dispute as to whether or not the flve-membered ring of the fluorenyl cation is antiaromatic. Clearly the antiaromatic character is less than for the indenyl or cyclopentadienyl cations, but current opinion favors antiaromaticity also for the fluorenyl cation.90 92 This is supported by the large difference in pAR from the anthracenyl cation, (although an additional reason for this difference will be noted later in the chapter, p. 61). Again, the brackets indicate correction of a measurement from TFE H20 to water. 

Adam, W. and Sendelbach, J., Photosensitized electron transfer form azoalkanes generation, fragmentation, and rearrangement of radical cations structurally related to dicyclopentadiene, /. Org. Chem., 58, 5310, 1993. 

The observation that very significant parts of the cocaine molecule could be deleted from synthetic analogs without loss of biologic activity led to the search for the minimal structural feature consistent with activity. This exercise, sometimes referred to as molecular dissection, not only led to great simpli-fi cation of the structure of local anesthetics but resulted fi-tially in the preparation of active molecules that bear only the remotest structural relation to the prototype, cocaine. 

Since hydrofluoride synthesis is based on thermal treatment at relatively high temperatures, the possibility of obtaining certain fluorotantalates can be predicted according to thermal stability of the compounds. In the case of compounds whose crystal structure is made up of an octahedral complex of ions, the most important parameter is the anion-cation ratio. Therefore, it is very important to take in to account the ionic radius of the second cation in relation to the ionic radius of tantalum. Large cations, are not included in the... 

The most intensively investigated dehydroxylation is probably the reaction of Mg(OH)2, though detailed results are also available for the hydroxides of certain other divalent cations. Several summaries of the mechanistic deductions obtained from such work, including literature sources, were presented at a conference at Dijon in 1974 [87]. The extensive literature concerned with the thermal analysis of hydroxides has been reviewed by Dollimore [79] who has also included the behaviour of oxides. Water elimination can be regarded as the first in a sequence of structurally related steps through which the hydroxide is converted into the thermally most stable oxide. 

Solid solutions are very common among structurally related compounds. Just as metallic elements of similar structure and atomic properties form alloys, certain chemical compounds can be combined to produce derivative solid solutions, which may permit realization of properties not found in either of the precursors. The combinations of binary compounds with common anion or common cation element, such as the isovalent alloys of IV-VI, III-V, II-VI, or I-VII members, are of considerable scientific and technological interest as their solid-state properties (e.g., electric and optical such as type of conductivity, current carrier density, band gap) modulate regularly over a wide range through variations in composition. A general descriptive scheme for such alloys is as follows [41]. 

Zeolites are structurally related to colorless sodalite, Na4Cl[Al3Si3012], and to deeply colored ultramarines. These have aluminosilicate frameworks that enclose cations but no water molecules (Fig. 16.25). Their special feature is the additional presence of anions in the hollows, e.g. Cl-, S()4, S2, or S. The two last-mentioned species are colored radical ions (green and blue, respectively) that are responsible for the brilliant colors. The best-known representative is the blue mineral lapis lazuli, Na4S (.[Al3Si3012], which is also produced industrially and serves as color pigment. 

Except for very electron-rich donors that yield stable, persistent radical cations, the ox values are not generally available.64 Thus the cation radicals for most organic donors are too reactive to allow the measurement of their reversible oxidation potentials in either aqueous (or most organic) solvents by the standard techniques.65 This problem is partially alleviated by the measurement of the irreversible anodic peak potentials E that are readily obtained from the linear sweep or cyclic voltammograms (CV). Since the values of E contain contributions from kinetic terms, comparison with the values of the thermodynamic E is necessarily restricted to a series of structurally related donors,66 i.e.,... 

The structurally related salts [M(Cp )2] [M (tds)2] (M = Fe, Mn, Cr M = Ni, Pt) and [Fe(Cp )2][Pt(tds)2] allowed a systematic study of the effect of a diversity of variables on the magnetic behavior of these compounds, such as the variation of the spin of the cation, the role of the single ion anisotropy, the effect of the variation of the size of atoms involved in the intermolecular contacts. Furthermore, the analysis of the intermolecular contacts in these compounds provided a reasonable interpretation of the intra and interchain magnetic coupling, and its relative strength within the series [44, 45]. 

The results obtained in combination with the data on the transformations of cations 9-11, led to the conclusion that 1,2-shifts of methyl groups occur readily in carbocations having a pentalene fragment. On the basis of the data obtained for rearrangements of such carbocations, an alternative mechanism has been proposed (52) for the rearrangement of structurally related carbocation 16 having a bicyclo[3.3.0]octane skeleton described in (33) (Scheme 12). 

EA are the ionization potential and electron affinity of the donor anions and acceptor cations, respectively, in the gas phase and wp represents the ion-pair interaction. (Note the ionization potentials in the gas phase parallel the anodic potentials in solution for structurally related electron donors the same interrelationship applies to electron affinities and cathodic potentials.) Accordingly, these coloured crystals are also referred to as charge-transfer salts (Wei etal., 1992). 

In the case of LDH hosts, since only the average structure is known, it is important to consider the local structure by means of X-ray absorption spectroscopy extended X-ray absorption fine structure (EXAFS). According to an ideal model based on edge-sharing octahedra [64], it is possible to define the local environment around each type of cation in relation to the layer-charge density. Figure 11 shows the local cation environment for LDH with... 

D. Solid State Structure of R3E Cations and Related Species. 190... 

This was in fact found to be the case when a similar approach to that employed for GPCRs was applied to ion channels. For example, the voltage gated cation channels belong to the largest group of structurally related ion channel proteins and were therefore chosen as the most amenable to analysis. However, a dichotomy exists, relative to the GPCRs, in terms of the... 

The structures of the ions rest on CIDNP spectra delineating their hyperfine patterns,ab initio calculations - ESR and ENDOR data for 16 +, and TR-ESR results for 15 +. Ab initio calculations (B3LYP/6-31G //UMP2/6-31G ) reproduce positive and negative hyperfine coupling constants satisfactorily. Each radical cation is related uniquely to the geometry of one of the precursors (Fig. 6.13). 

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