Potassium placement

One case of n—5 —n delocalization was demonstrated by Stevenson et al. (2006). The potassinm anion-radical salt of l-(9-methyl-9H-fluoren-9-yl)-4-methyl benzyl is characterized by the delocalization of an nnpaired electron within the fluorenyl moiety only. Its ESR spectrnm completely coincides with the spectrnm of the potassium anion-radical salt of the 9,9-dimethyl fluorene anion-radical in THE However, the cesium anion-radical salt of the fluorenyl methylbenzyl derivative produces the ESR spectrum corresponding to the placement of this cation between the fluorenyl and methylbenzyl moiety. The conditions of n—s—n delocalization appear An unpaired electron spends its time within both fluorenyl and methylbenzyl fragments. The situation is explained in Scheme 3.54. 

Flowers were produced by the unsprayed plants that were exposed for only 30 short days. This confirms that flowers had been initiated in the crowns of plants when sprays were applied after 30 short days and that these plants represented a different population from those sprayed immediately on placement under short-day conditions. One clearly evident result was a sharp reduction in number of flowers produced. The plants treated with 10 p.p.m. of potassium gibberellate, regardless of time, produced about one half as many flowers as the control plants. This was not observed in the field studies at the 10-p.p.m. concentration, but 40 p.p.m. of potassium gibberellate used three times in the field reduced yields by about one half. 

It is instructive to compare the -OSO2F group observed here with the SOaF ion observed in the potassium " and ammonium salts. Although there is evidently disordering of the O and F placement of the sulfur ligands in the anion in the potassium salt and partial disordering in the ammonium salt, ion dimensions were determined for each case, assuming C3. sjmi-metry of the disordered ion. 

In a companion paper Price and Akkapeddi [22] report the kinetics of base initiated polymerization of epoxides in DMSO and hexamethyl-phosphoramide (HMPT). The initiator is potassium t-butoxide. Second order rate coefficients for (R,S)—PO were about double those for (+)—(R) or (—)—(S) monomer. They conclude that the steric factor favouring alternation of isotactic and syndiotactic placement of the t-BuEO also influences PO. Chain transfer to solvent (DMSO) was also studied. For PO polymerization in DMSO they obtain k = 1.5 x 10 exp(—17,200/RT). However, due to some erratic results they are not very confident about the accuracy. In HMPT rates are about three fold faster than in DMSO k = 7.3 X 10 exp(—16,300/RT). Three other epoxides were also studied in HMPT EO, k = 2.75 x 10 exp(-13,300/RT) t-BuEO, fe = 2.0 x 10 exp(-17,100/RT) phenylglycidyl ether (PGE), fc = 5.4 x 10" ... 

The placement and motion of potassium ions as well as the distortion of the polymer chains have been addressed by Corish el al. (see [116] and references therein), using atomistic lattice simulations. 

The anionic polymerization of propylene oxide initiated by potassium alkoxide or hydroxide occurs predominantly (95%) by cleavage of the O-CH2 bond. For bulk polymerization at 80 °C, approximately 4% head-to-head placements occur. However, there is no stereocontrol in this alkoxide-initiated ring opening and the resulting polymer is nontactic [140]. 

Formation of such intermediates is favorable for lithium because it has a small ionic radius and is high in the proportion of p-character. Organometallic compounds of the other alkali metals (sodium, potassium, rubidium, and cesium) are more polar and more dissociated. They react essentially as solvated ions even in a hydrocarbon medium, yielding high 3,4 placement. 

These 5- l bonds are largely responsible for the oval shape of uncomplexed valinomycin. Moreover, they direct two of the ester carbonyl oxygens toward the surface of the molecule (see Fig. 4). These might serve as initiators of complex formation by interaction with the metal ion prior to the placement of the latter in the ligand cavity. Based on this assumption. Smith and Duax developed a simplified model for the complexation process They proposed that the formation of the initial loose complex with the potassium ion is followed by cleavage of both the 5->l type hydrogen bonds in order to enable all the other ester carbonyl oxygens to interact with the cation and to replace the molecules of its solvation shell one after another. 

Some of the advantages of this type of sensor were already anticipated in one of the earliest FIA applications, namely, the joint determination of sodium and potassium in serum. Important parameter include the angle at which the carrier impinges on the active surface, the electrode placement angle, the immersion depth and surface area, the flow rates, and the cell void volume. 

Figure 9 shows several TPD spectra of mass 31 (P) at different exposure times to calcium phosphate solution (55). Phosphorus desorption from alumina riiows broad features from 450-700 K, the residual salt peak at 980 K, and a high tenq>erature feature, vAach occurs between 1400 and 1560 K. Variation in the tenq>erature associated with the high tenq)erature desorption feature may be a result of variations in heating rate or thermocouple placement. Unlike the titania spectra, the large feature at 1200 K is absent. In addition, at least one new feature can be observed at approximately 450-700 K Figure 9b shows the corre onding calcium and potassium desorption features. The ratio of calcium and potassium ions to pho horus is conq)arable, but for longer exposures, this ratio decreases dramatically. For a 30 hr. e q>osure, the calcium and potassium to phosphorus ratios drop to less than 1% of the solution concentration. Integration of several phosphorus desorption ectra provide the data for an adsorption isotherm shown in Figure 8. Onset of rapid uptake of pho hate is observed between 20-25 hr.

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