Functional groups of type

Functional groups of type E which confer electrophilic character upon the ipso carbon atom to which they are attached. 

Functional groups of type N or G (after Seebach [16],1979) that -in contrast with the type E- confer nucleophilic character upon the ipjo-carbon atom to which they are attached. 

Functional groups of type A, which exhibit an ambivalent character, conferring both electrophilic and nucleophilic character upon the carbon atom to which they are attached. Whichever character is manifested will depend upon the reaction conditions and/or the structure of the molecule to which the functional group is attached. 

With regard to functional groups of type A, their interest lies in the ambivalent character exhibited by such groups, which not only confer a double electrophilic and nucleophilic character to each of the carbon atoms of the carbon chain, but they may even violate, in some cases, the rule of alternating polarities postulated by Lapworth. 

Bifunctional systems In the case of bifunctional systems (or molecules) only two alternatives are possible the bifunctional relationships are either "consonant" or "dissonant" (apart from molecules or systems with functional groups of type A to which we have referred to as "assonant"). In the first case, the synthetic problem will have been solved, in principle, in applying the "heuristic principle" HP-2 that is to say, the molecule will be disconnected according to a retro-Claisen, a retro-aldol or a retro-Mannich condensation, or a retro-Michael addition, proceeding if necessary by a prior adjustment of the heteroatom oxidation level (FGI). 

Notice that the final result is a 1,3 charge affinity inversion Umpolung) of an allylic derivative via a FGI of a functional group of type E by a group of type A, followed by a [2,3]-sigmatropic rearrangement. If the intermediate allyl anion reacts with a carbonyl compound as the electrophile the result is then a 1,4-D system, such as ... 

HP-7 Heterolytic disconnection of the appendages directly attached to sp carbon atoms bearing functional groups of type E and eventually of type A. 

A polymerization that provides a transition into a discussion of gelation is the condensation of an excess of A-B with a small amount of an /-functional monomer, R-A/, that contains / equivalent functional groups of Type A, but no functional groups of Type B.[3 Linear chains are obtained when / is 1 or 2, but multichain condensation polymers are produced when/>2. At high conversion the polydispersity index depends only on/. 

Another reaction that does not lead to gelation is the polymerization of hyperbranched polymers from ABy, monomers (each with a single functional group of type A and/— 1 functional groups of type B) in which A can only react with B. For functionality f=2, this reduces to the condensation polymerization of linear chains, described above. For... 

In these equations, the subscripts c, b, and/indicate the critical point, boiling point, and freezing point, respectively the A terms are the contributions of the group to each of the specifieAproperties given in the following table and v, is the number of functional groups of type i in the molecule. 

Consider a polymerization that forms AB links and in which % < where is the number of equivalents of the functional groups of type i. In this case, the number... 

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