Substituent groups radicals

Substituent groups ( radicals ) derived from acids and certain derivatives thereof by removal of -OH from the functional group are generally called acyl groups and individually named by transforming the ending... ic acid to. ..yl or. ..oyl and. ..carboxylic acid to. ..carbonyl. The names thus formed can also be used in radicofunctional (functional class) nomenclature. 

I The phenol cannot always be isolated in good yield, particularly if it contains substituent groups, owing to the destructive action of the alkali fusion upon the radical R. 

Radicals from Ring Systems. Univalent substituent groups derived from polycyclic hydrocarbons are named by changing the final e of the hydrocarbon name to -yl. The carbon atoms having free valences are given locants as low as possible consistent with the fixed numbering of the... 

For most vinyl polymers, head-to-tail addition is the dominant mode of addition. Variations from this generalization become more common for polymerizations which are carried out at higher temperatures. Head-to-head addition is also somewhat more abundant in the case of halogenated monomers such as vinyl chloride. The preponderance of head-to-tail additions is understood to arise from a combination of resonance and steric effects. In many cases the ionic or free-radical reaction center occurs at the substituted carbon due to the possibility of resonance stabilization or electron delocalization through the substituent group. Head-to-tail attachment is also sterically favored, since the substituent groups on successive repeat units are separated by a methylene... 

The nature of the secondary reactions is uncertain. Some beheve that the primary tar components are broken down to small free radicals that recombine as they travel toward the retort exit others suggest that some components remain relatively intact except for the removal of peripheral substituent groups and that the higher molecular weight components of coal tar are, in effect, slightly altered fragments of the original coal stmcture. 

Another quite general source of free radicals is the decomposition of azo compounds. The products are molecular nitrogen and the radicals derived from the substituent groups ... 

Both symmetrical and unsymmetrical azo compounds can be made, so that a single radical or two different ones may be generated. The energy for the decomposition can be either thermal or photochemical. In the thermal decomposition, it has been established that the temperature at which decomposition occurs depends on the nature of the substituent groups. Azomethane does not decompose to methyl radicals and nitrogen until temperatures above 400°C are reached. Azo compounds that generate relatively stable radicals decompose at much lower temperatures. Azo compounds derived from allyl groups decompose somewhat above 100°C for example ... 

Names for radicals are formed in the same way as those for the corresponding substituent groups (see 2-Carb-31.2). 

Maleimides Alkyl and aryl maleimides in small concentrations, e.g., 5-10 wt% significantly enhance yield of cross-link for y-irradiated (in vacuo) NR, cw-l,4-polyisoprene, poly(styrene-co-butadiene) rubber, and polychloroprene rubber. A-phenyhnaleimide and m-phenylene dimaleimide have been found to be most effective. The solubihty of the maleimides in the polymer matrix, reactivity of the double bond and the influence of substituent groups also affect the cross-fink promoting ability of these promoters [82]. The mechanism for the cross-link promotion of maleimides is considered to be the copolymerization of the rubber via its unsaturations with the maleimide molecules initiated by radicals and, in particular, by allyfic radicals produced during the radiolysis of the elastomer. Maleimides have also been found to increase the rate of cross-linking in saturated polymers like PE and poly vinylacetate [33]. 

Substituent groups on a polyphosphazene chain containing mobile hydrogen atoms (4-isopropylphenol [715,716], 4-benzylphenol [293,718], etc.) showed a completely different photochemical reactivity both in solution and in sohd state under accelerated conditions, based mostly on the fight-induced oxidation of these groups and radical formation reactions. 

It is important to emphasize the solvent dependence of nitroxide esr spectra. The aN-value may increase by nearly 20% on transferring a given radical from a hydrocarbon solvent to water, and the use of, for example, di-t-butyl nitroxide as a probe for solvent properties has been advocated (Knauer and Napier, 1976 Lim et ah, 1976). The magnitudes of splittings from atoms in substituent groups are also solvent-dependent. 

This shows that the change 8Fg is independent of the sign of the electronegativity change produced by the substituent group, a result in accord with the experimental flndings mentioned in Section IIB, and lends support to the notion that Fg is a useful index for free radical attack. 

Previously, it was mentioned that the steric characteristics of the carbon atom (primary, secondary, tertiary) should be considered it becomes clear with the new classes of compounds studied that the electronic characteristic of the substituent groups—aryl, hydroxyl, alkoxyl— must also be taken into account. Thus, whereas trisalkylperoxy radicals have weak recombination constants, dialkylhydroxy or dialkylalkoxy have much higher recombination constants, occasionally similar to values observed for secondary alkyl radicals. 

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