Rigid compounds

For this reason tribasic lead sulphate, a good heat stabiliser which gives polymer compounds with better electrical insulation properties than lead carbonate, has increased in popularity in recent years at the expense of white lead. Its weight cost is somewhat higher than that of lead carbonate but less than most other stabilisers. This material is used widely in rigid compounds, in electrical insulation compounds and in general purpose formulations. 

The separation of formal charges in a polar limiting structure like 2b creates a dipole moment of ca. 20 D. Therefore, if such structures were of great importance, quite high dipole moments should be expected for push-pull ethylenes. Data for a reasonable number of mostly symmetrical and rather rigid compounds are known (Table 20). Several high dipole moments are observed, though not in the vicinity of those required for a complete transfer of the double-bond it... 

The first dataset consisted of 91 rigid compounds (mono- and di-substituted benzenes, polycyclic aromatic hydrocarbons, cyclic amides, and pyrazole and imidazole derivatives) selected from the WDI on the basis of a count of the number of rotatable bonds computed using TSAR none of the 91 structures had rotatable bonds. The structures are listed in Table 1 together with their experimental log Poct values, which cover a range from -2.17 to +6.5 the values were retrieved from the SRC web site (27). 

Padwa et al. (187,188) concisely summarized his domino cycloaddition/ A -acyliminium ion cyclization cascade process, which involves sequentially the generation of an isomiinchnone 1,3-dipole, intramolecular 1,3-dipolar cycloaddition reaction, 77-acyliminium ion formation, and, hnally, Mannich cyclization. Kappe and co-workers (189) utilized Padwa s cyclization-cycloaddition cascade methodology to construct several rigid compounds that mimic the putative receptor-bound conformation of dihydropyridine-type calcium channel modulators. 

Portoghese and coworkers also considered other naltrindole derivatives substituted in position 6 or 7 with aryl, benzyl or aniline moieties to evaluate the effect of flexible aryl groups on selectivity, but obtained non-selective compounds only. This result demonstrates that the conformational flexibility of these aryl groups causes them to reside preferentially in regions of space that are not accepted by the 8 opioid receptor (Portoghese et al., 1994). A more rigid compound however, 7-benzylidene-naltrindole (BNTX) proved to be a potent and highly... 

PVC has a unique ability to be compounded with a wide variety of additives, making it possible to produce materials that range from flexible elastomers to rigid compounds, that are virtually unbreakable. Compounds arc also made that have stiff melts for profile extrusion or low viscosity melts fur thin-walled injection molding. 

Scheme 10 Cyclodextrins as Homologous Cyclic Oligosaccharides Are Highly Symmetrical and Rigid Compounds and Are Ideal Templates for the Construction of, for Example, Hexameric Peptide Assemblies on a-...

The compounds we examined in extrusion rheometer and in plastograph had the same recipe as that adopted for determining the physical-mechanical characteristics. However, extrusions were carried out with rigid compounds having an industrial recipe suitable for pipes and sections. Gelation of the dry blend, obtained by turbomixer (10 minutes at 1800 rpm, max. temp. 100°C) was carried out by two-roll mill for 10 minutes at 180°C the blank sheets were mechanically granulated. 

Prinzbach and co-workers studied the photocycloaddition of a rigid compound in which naphthalene and alkene were placed [294], Distances between naphthyl (3-carbons and olefinic carbons of 272 are 2.911 and 2.944 A. Direct or acetone-sensitized photoexcitation induced an efficient meta addition to the naphthalene ring to give 273, the ortho addition did not occur, although it is not clear whether the ortho process occurred (Scheme 76). 

Vicinal Carbon-Proton Coupling Constants for Different Dihedral Angles of C—O—C—H Arrays of Bonded Atoms, Measured from Spectra of Rigid Compounds in Natural Abundance... 

Typical applications of the method are cases where conventional high-resolution NMR parameters do not provide sufficient configurational information or when the precise conformation of a molecule in solution is desired. Impressive examples for the power of RDCs have been reported for the determination of relative configurations in natural products and for conformational studies of sugars and peptides. While initial studies have been limited to rigid compounds, now also more and more flexible molecules are investigated. 

ASTM D1784 PVC rigid compound cell classification... 

The anti-periplanar confonnation is more stable because it is staggered rather than eclipsed. Therefore, anti elimination is preferred in the E2 reaction. (Syn elimination is much less common but does occur when the leaving group and the hydrogen are held syn-periplanar in an eclipsed, or nearly eclipsed, confonnation of a rigid compound.) The elimination reactions of the diastereomers of l-bromo-l,2-diphenylpropane are illustrated in Figure 9.2. 

---