Substitution chain

Fluorination presents problems of the other extreme. Both steps in the substitution chain reaction are so exothermic that the reaction is violent if not performed under carefully controlled conditions. Furthermore, fluorine atoms are capable of cleaving carbon-carbon bonds ... 

The reaction of a chain radical with a unit of a previously formed polymer represents an additional possible chain transfer process not previously considered in Chapter IV. The point of attack might again be located in the substituent X, or it might involve removal of the tertiary hydrogen on the substituted chain carbon. The following sequence of reactions, in which the latter alternative has arbitrarily been assumed, would then lead to a branched polymer molecule as indicated. ... 

B.2.9-12.) The interaction between an o-methyl group and an a cr-di-methyl-substituted chain is particularly severe, and undoubtedly leads to restricted rotation about the ring-chain bond (see Lomas and Dubois, 1978). This is not itself a major source of high effective molarities, however, as shown by the moderate EM s for compounds like [20] and [21] which have naturally restricted conformations (Danforth et ai, 1976). 

Figure 4. Single worm-like polymer chains of den-dronized polystyrene deposited on pyrolytic graphite, imaged by topographic scanning force microscopy (SFM) [24 the inset illustrates the structure of the den-dron-substituted chains...

The results show that the presence of bulky substituent on a polymer chain may effectively inhibit the termination proceeding by this mechanism. The results presented at this point may be summarized as follows chain transfer to polymer is a general feature of cationic ring-opening polymerization although for different systems the contribution of this reaction may vary only in some systems this process results in termination (These systems involve, e.g., cyclic amines (3- and 4-membered) and cyclic sulfides (3- and 4-membered) and the contribution of the reaction is reduced for substituted chains. 

Chain Reactions Substitution Chain, Addition Chain, Polymerization Chain... 

Predict the major radical substitution chain products of 1-phenylpropane heated with f-butyl hypochlorite. 

Interestingly, bacteria very often contain not only these n-acyl amphiphiles, but largely, or even mostly, mixtures of analogs with branched chains (e.g. iso- or ante-iso-, or cyclopropyl- or co-cycloalkyl-substituted chains). However, the biosynthetic processes required are again very complex. 

An important constituent of all fatty acids and their derivatives is the alkyl chain. These chains vary in length (number of carbons) and in the extent of branching and polar group substitution. Chains also vary in the type, number, position, and geometric configuration of unsaturated carbon-carbon bonds. Such differences in alkyl chain structure are largely responsible for the broad variation in the biological properties of... 

Methyllithium reacts with (NPp2) by a complex process that includes substitution, chain cleavage and crosslinking via metallation of methyl groups attached to the skeleton . 

Acrivastine, an acidic congener of triprolidine in which a carboxylic acid-substituted chain has been attached, also is a second-generation, nonsedating antihistamine. Penetration of the blood-brain barrier is limited, and it is less sedating than triprolidine. It is used principally in a combination with a decongestant. 

Taken together, these three parameters allow comprehensive stereochemical analysis of complex natural products. Each diastereomer can be described as a combination of three staggered rotamers, a reasonable approximation for a variety of hydroxy and methyl substituted chains, in the absence of bulky substituents. Four out of the six rotamers for a threolerythro pair of diastereomers can be determined unambiguously solely from the three coupling constants discussed therein. The remaining pair of conformations can be distinguished on the basis of NOEs. 

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