Undecyl radicals

Allyl radicals can, of course, also be generated by electrolysis of the corresponding /J,y-unsaturated carboxylic acids together with a second carboxylic acid. This mixed Kolbe electrolysis method has been used to study the recombination of allyl radical 32 with the undecyl radical 3370. Recombination leads to the formation of adducts 34 and 35 in a ratio of 72 28, again preferring the product with the higher substituted double bond (equation 16). 

EPR spectra obtained after y-irradiation of undecane at various concentrations in CCI3F are shown in Fig. 5.6. With increasing undecane concentration, the disappearance of undecane radical cations and transformation of primary into secondary undecyl radicals (by intermolecular radical-site transfer)... 

The transformation of primary into secondary undecyl radicals and the dominance of secondary undecyl radicals at much higher concentrations unequivocally show that, as a rule, undecane aggregates in CCI3F are amorphous and this conclusion can reasonably be extended to all n-alkanes with Hq < 11 for concentrations below about 20 mol%. In the EPR spectra of y-irradiated CCl3F/undecane primary radical features reappear from about 7 mol%, however, and these features... 

Fig. 5. Hammett equation plot of relative k values vs. a for hydrogen abstraction from substituted toluenes by the undecyl radical at 3S4 K. The least-squares treatment gives p = 0.50(2) (r = 0.97) [74 Pry 1]. /, 4-methyltoluene 2, 3-methyltoluene S, toluene 4, 4-fluorotoluene 5, 4-chlorotoluene 6, 3-fluorotoluene 7, 3-chlorotoluene 8, 3-cyanotoluene 9,4-methoxytoluene /0,4-r-butyltoluene //, 3-methoxytoluene 12,3-bromotoluene.

This was utilized by Tian et al. [168] to prepare a new class of liquid crystal homopolymers of poly ll-[4-(3-ethoxycarbonyl-coumarin-7-oxy)-carbonyl-phenyloxy]-undecyl methacrylate] containing a coumarin moiety as a photocross-linkable unit. The preparations included polymers of various chain lengths. Also, hquid crystaUine-coil diblock and hquid crystalline-coil-liquid crystalline triblock copolymers with polystyrene as the coil segment were formed. The polymers were reported to have been synthesized with the aid of atom transfer radical polymerization. The dimerization of the coumarin moieties takes place upon irradiation with light of A > 300 nm to yield cross-linked network structures. 

Liquid crystalline amphiphilic diblock copolymers poly(ethylene oxide)-h/oc -ll-[4-(4-butylphenyl-azo)phenoxy]-undecyl methacrylate, PEOn,-h-PMA(Az) , as shown in Fig. 16, prepared by atom transfer radical polymerization [61], were composed of hydrophilic PEOn, sequences and hydrophobic PMA(Az) , with azobenzene moieties such as mesogen connected by a flexible spacer. The synthesis of such amphiphilic liquid crystal block copolymers has been recently reported [62]. In diblock copolymers PEO ,-h-PMA(Az)n, m and n indicate the degree of polymerization of PEO and PMA(Az) components, respectively. Differential scanning calorimetry (DSC) of PEO ,-f>-PMA(Az)n gives a clear picture of the thermal properties of these liquid crystaUine polymers, as shown in Fig. 17, for PEOn4-h-PMA(Az)2o [58, 61]. 

Irradiation of 1,3-dioxolanes in the presence of a sensitizer such as benzophenone (PhjCO), leads to the abstraction of an acetal hydrogen atom (by the triplet state ketone) to generate 1,3-dioxolanyl radicals, together with the resonance-stabilized diphenyl ketyl radical (Scheme 16). These nucleophilic 1,3-diox-olanyl radicals have been shown to add to a variety of alkenes to form adduct radicals, which can then accept a hydrogen atom from the diphenyl ketyl radical to give the desired alkylated product. The diastereoselective addition of 1,3-dioxolanyl radicals to alkenes bearing chiral auxiliaries has also recently been reported, while the photochemical alkylation of diketene with 2-undecyl-l,3-dioxolane has been utilized as a key step in the synthesis of (-)-tetrahydrolipstatin (Scheme 17). ... 

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