Delocalizing substituents

These observations clearly support the naive idea that the para substituents exert almost no effect at remote carbenic center of brominated DPCs, at least in terms of steric congestion. Furthermore, electronic effects do not seem important enough to change the reactivity of brominated DPCs so significantly. For example there is rather small distribution in the Hammett and spin-delocalizing substituent constants. 

Several 2,6-disubstituted adamantane-2,6-diyl dications 181 have been prepared and characterized.398 They are stable only when they contain charge delocalizing substituents such as cyclopropyl or phenyl groups. Recently, a DFT... 

As expected, delocalizing substituents such as carbomethoxyl and cyano should decrease the barrier to inversion and perhaps may even convert the rapidly inverting g radical to a linear n radical. The net result should be a loss of configuration. Ando and coworkers have shown this to be the case in the tri-n-butyltin hydride reduction of the isomeric exo- (38) and n io-7-chloro-7-carbomethoxybicyclo[4.1.0]heptane (39). Both isomers gave the same (7 93) ratio of exo- (40) and emio-methyl bicyclo[4.1.0]heptane-7-carboxylate (41). 

The most common initiators of cationic polymerization are Lewis acids, such as AlCl3,BF3,SnCl4, and TiCU, although strong protic acids such as H2SO4 may also be used. Cationic polymerization is restricted to vinyl monomers with electron-donating or electron-delocalizing substituents, e.g., isobutylene, vinyl... 

Diphenyl porphyrins and their Zn° complexes substituted in the meso position by a Jt-delocalized substituent carrying an electron-donor or an electron-withdrawing group (49) were also investigated by the EFISH technique [169]. These second-order NLO chromophores have confirmed the ambivalent role of the polarizable porphyrin ring, which, in the ground state, already acts as a donor or acceptor. 

Figure 11.38 Effect of additional delocalizing substituents on regioselectivity of C-H insertion.

The synthesis of anionic compounds derived from squaric acid possessing one or more jt-delocalized substituents, such as dicyanomethylene groups. 

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