Nucleophilic and Radical Additions

Although a large number of isomers are in principle possible for additions of segregated addends, the preferred mode of addition is 1,2. For a combination of sterically demanding addends 1,4 additions [63,66,72,75,80] and even 1,6 additions [87] (to the positions 1 and 16) can take place alternatively or exclusively (Fig. 7). 

The addition of free radicals like R3C , R3Si, R3Sn and RS generated chemically, photochemically, or thermally leads also to substituted dihydro- or polyhydrofullerenes, with the same preferences of addition modes [88-93]. As far as the resulting addition patterns of products and the presumed mechanisms are concerned, nucleophilic additions and radical additions are closely related and in some cases it is difficult to decide which mechanism actually 

This implies a useful approximation, namely to look at a 1,2-dihydro [60]-fullerene as a stereoelectronically slightly perturbated 50. The introduction of a double bond into a five-membered ring costs about 8.5 kcal/mol [3, 103] (Figs. 9 and 10). In a 1,4-adduct (1,4-dihydro[60]fullerene) one and in a 1,6-adduct (1,16-dihydro[60] fullerene or 1,6-dihydro [60]fullerene) two bonds in five-membered rings are required for the corresponding lowest-energy Kekule structure. This VB consideration is also confirmed experimentally and by computations (Fig. 7). 

4 and 1,16 addition patterns are only preferred for sterically demanding addends, since in the corresponding 1,2-adducts or even in some 1,4-adducts the eclipsing interactions become predominant (Table 3). A 1,6-addi-tion pattern with a cluster closed structure is unfavorable and has never been isolated due to both introduction of two [5,6]-double bonds and eclipsing interactions. In 1,2-C6oH2, the eclipsing interaction was estimated to be about 

3-5 kcal/mol. This value increases with an increasing size of the addend. The 

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Figure 11.21 Some examples of displacemment of the terminal halogen in ATRP polymers using electrophilic, nucleophilic, and radical (addition) reactions. (Adapted from Matyjaszewski andXia, 2001.)...

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