Shielded derivatives

Rb NMR shieldings have been shown experimentally to depend linearly on the distance of the Rb" ion to its nearest neighbor shell of halide ions in the family of Rb-doped alkali halides, and theoretical calculations bear out the experimental linear trends. The shielding derivatives with respect to the ionic distance are positive and are very similar, largely independent of the identity of the halide ion for the distances that naturally occur in the alkali halide lattices. At much shorter distances, we would not expect this to be the case. 

Fig. 2. Detoxication of cysteine by its conversion to a shielded derivative. The figure shows hydrogenation runs carried out (a) with the poison in its original form, (b) with the poison after detoxication, and (c) with a hydrogenation system containing no poison.

The conversion of thiophene into a shielded derivative (Maxted, 14) thus involves the application of a two-stage process consisting of a preliminary hydrogenation step (which, in practice, may be of very short duration, e.g. 2-3 minutes) followed by the addition of a small quantity of an oxidizing detoxicant. The course of the detoxication is therefore ... 

This use of a relatively high hydrogenation temperature with nickel raises the important question of the stability at high temi ratures of the various shielded derivatives, principally sulfonic acids or sulfones, into which sulfur-containing catalyst poisons are converted by detoxication processes. It should however be pointed out that this question of stability will not in any case affect the use of detoxication methods for... 

Table 1. F Absolute Isotropic Shielding of the Rovibrationally Averaged Free Molecule at 300 K Based on HF Molecule, Compared with Absolute Shielding Derived from...

The plutonium extracted by the Purex process usually has been in the form of a concentrated nitrate solution or symp, which must be converted to anhydrous PuF [13842-83-6] or PuF, which are charge materials for metal production. The nitrate solution is sufficientiy pure for the processing to be conducted in gloveboxes without P- or y-shielding (130). The Pu is first precipitated as plutonium(IV) peroxide [12412-68-9], plutonium(Ill) oxalate [56609-10-0], plutonium(IV) oxalate [13278-81-4], or plutonium(Ill) fluoride. These precipitates are converted to anhydrous PuF or PuF. The precipitation process used depends on numerous factors, eg, derived purity of product, safety considerations, ease of recovering wastes, and required process equipment. The peroxide precipitation yields the purest product and generally is the preferred route (131). The peroxide precipitate is converted to PuF by HF—O2 gas or to PuF by HF—H2 gas (31,132). 

The auto industry has estabbshed a cooperative program in the field, the Vehicle Recycling Partnership (VRP). In addition, some auto manufacturers have announced specific projects that include recycled mbber. Chrysler has announced that it is already using a mbber shield that incorporates cmmb mbber derived from scrap tires. Auto manufacturing companies have indicated a desire to expand the use of recycled post-consumer scrap mbber in their products. 

The toughness induced in ceramic matrices reinforced with the various types of reinforcements, that is, particles, platelets, whiskers, or fibers, derives from two phenomena crack deflection and crack-tip shielding. These phenomena usually operate in synergism in composite systems to give the resultant toughness and noncatastrophic mode of failure. 

Kermisic Acid. Many accounts claim that kermisic acid [476-35-7] (Cl Natural Red 3 Cl 75460) is the oldest dyestuff ever recorded (23). The name kermes is derived from an Armenian word meaning Httle worm for which the later Latin equivalent was vermiculus, the basis of the Knglish word Vermillion. The dye was obtained from an oriental shield louse, K. ilicis which infest the holm o5kQuercus ilex and the shmb oak. coccifera. The dye produces a brilliant scarlet color with an alum mordant. Although expensive, it was cheaper than its rival Tyrian Purple. It was in great demand until the sixteenth century when it was displaced by carminic acid. 

In deuterochloroform, pyrazine shows a single proton resonance at S 8.59 (72CPB2204). Vo, Vm and Vp values between pyrazine ring protons obtained from a number of pyrazine derivatives are 2.5-3, 1.1-1.4 and 0 Hz respectively, and these values do not appear to be affected by the nature of the ring substituents. Some substituent shielding parameters are shown in Table 1. 

The theory for plane jets is similar to descriptions of circular jets (see Section 7.4) and many derived equations describe both two-dimensional (plane) and three-dimensional (round) jets. The principle is to generate such high air velocity that a shield against pressure difference, temperature difference, and wind velocity is sustained. Howeveg it is not possible to have complete separation by an air curtain. The main reason for this, is that the jet entrains air... 

---