Orientation substitution

The ring-chlorinated derivatives of toluene form a group of stable, industrially important compounds. Many chlorotoluene isomers can be prepared by direct chlorination. Other chlorotoluenes are prepared by indirect routes involving the replacement of amino, hydroxyl, chlorosulfonyl, and nitro groups by chlorine and the use of substituents, such as nitro, amino, and sulfonic acid, to orient substitution followed by their removal from the ring. 

Tacticities of the polypropylenes above 60% [mmmm] highlights the tendency of the backward oriented substitution (4a) to produce plastomeric materials. During experiments in liquid propylene, no similarity is observed between the two isomeric catalysts. Catalyst 4b/borate does not follow the same trend in the catalytic performance as previously mentioned, but leads to polypropylenes with sufficient amount of isotactic sequences and relatively high molecular weight for the design of plastomeric polypropylenes. 

P. Dyreklev, M. Beggren, O. Inganas, M.R. Andersson, O. Wennerstrom, and T. Hjertberg, Polarized electroluminescence from an oriented substituted polythiophene in a light emitting diode, Adv. Mater., 1 43-45, 1995. 

There is a significant gap of degradation rates and performance properties between the aliphatic and aromatic polyesters. However, taking some hints from nature can fill this gap. Mixtures of polyesters, molecular orientation, substitution of some functional groups, and macro structures have all been proposed as a means to provide a range of application performance properties versus degradation rates. 

Most work, however, has been done on systems with several substitution sites. Formylation of the thieno[2,3-6]pyrroles (389) and (390) showed that in the former case, formylation takes place predominantly (90%) at C-5, and 10% at C-4. An electron-attracting substituent at C-5, as in 390, orients substitution into the thiophene ring (95% at C-2).407... 

Electron donor 2-substituents orient substitution in furan, thiophene and selenophene into the 5-position. In pyrrole, although the ratio of a to (3 reactivity is much smaller than in the other five-membered rings, 5-substituted 2-alkylpyrroles still appear to be the major products. 

Both groups are deactivating, but they orient substitution toward the same positions. 

The methods commonly used for chain alignment in polymer films have been reviewed [34]. They comprise the Langmuir-Blodgett technique, rubbing of the film surface, mechanical stretching of the film, and orientation on prealigned substrates. As an example, electroluminescence spectra of the oriented substituted poly(p-phenylene) presented in Chart 6.5 are shown in Fig. 6.9 a [35]. 

Chart 6.5 Chemical structure of an oriented substituted poly(p-phenylene) [35]. 

Fig. 6.9 (a) Electroluminescence spectra of the oriented substituted poly(p-phenylene) SPPP. The emission spectra were recorded with the polarization direction parallel and perpendicular to the dipping direction... 

Here G(f2) is a molecular normalized distribution with respect to the solid angle which defines the average over all the possible orientations. Substituting the expression for the induced electric dipole jlind, one gets ... 

Performing synthesis in two stages (where in the former stage a catalyst that orients substitution in the ortho position is used, and the latter stage uses an acid as catalyst) provides the formation of a reaction product the isomeric composition of which is similar to novolac obtained by acid catalysis (o-, p-isomer 80%). 

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