Fragmentation reactions of radical anions (mesolytic cleavages) of cyanobenzyl alkyl ethers (intramolecular dissociative electron transfer, heterolytic cleavages) have been studied electrochemically. The intrinsic barriers for the processes have been established from the experimental thermodynamic and kinetic parameters. These values are more than 3 kcal/mol lower as an average than the related homolytic mesolytic fragmentations of radical anions of 4-cyanophenyl ethers. In the particular case of isomers 4-cyanobenzyl phenyl ether and 4-cyanophenyl benzyl ether, the difference in intrinsic barriers amounts to 5.5 kcal/mol, and this produces an energetic crossing where the thermodynamically more favorable process (homolytic) is the kinetically slower one. The fundamental reasons for this behavior have been established by means of theoretical calculations within the density functional theory framework, showing that, in this case, the factors that determine the kinetics are clearly different (mainly present in the transition state) from those that determine the thermodynamics and they are not related to the regioconservation of the spin density ("spin regioconservation principle"). Our theoretical results reproduce quite well the experimental energetic difference of barriers and demonstrate the main structural origin of the difference.

Density functional theory electronic structure calculations of the homolytic/heterolytic aniomesolytic C-O fragmentations in the gas phase of a series of radical anions of substituted-phenyl benzyl ethers and substituted-benzyl phenyl ethers have been carried out. Along the series, the electron-withdrawing strength of the substituents increases. An intramolecular electron transfer from the pi system to the sigma molecular orbital of the scissile C-O bond is required to produce the fragmentation. As the electron-withdrawing strength of the substituents increases, the transition-state structures appear later with higher potential energy and Gibbs free energy barriers. The homolytic mesolytic cleavages are always thermodynamically favored versus the corresponding heterolytic mesolytic ones. The heterolytic mesolytic fragmentations in radical anions containing only weak electron-withdrawing groups are faster than the corresponding homolytic mesolytic ones. Conversely, in radical anions supporting strong electron-withdrawing groups the homolytic mesolytic fragmentations are faster in terms of potential energy barriers. However, the entropic contribution makes it comparable the homolytic and the heterolytic Gibbs free energy barriers in this case. The main factors that determine the relative rates of those kind of aniomesolytic cleavages are discussed.

a b s t r a c tThe objective of this paper is to compare the influence of two electron-withdrawing groups in the fragmentation of 2-methoxy-4-nitrophenyl benzyl ether and 4-cyanophenyl benzyl ether once these species are reduced. The stability of the corresponding radical anions depends essentially on those substituents. In our design we have chosen two species that are able to attach the electron but which have each a different capacity to retain it. An experimental study is carried out by EPR spectroscopy to analyze the different electronic nature of the generated radical anions. In addition, electronic structure calculations at the DFT level of theory have been performed to study those radical anions and their fragmentation pathways. The thermodynamics and kinetics of the two fragmentations are discussed and compared in detail.

This experiment studied the effect of broiler breeder nutritional strategies on uniformity, carcass traits, tibia parameters, and behavior during rearing and prebreeder periods (up to 22 wk of age). One-day-old pullets (n = 384) were randomly assigned to 4 treatments arranged as a 2 × 2 factorial, with 2 fiber levels (control vs. fibrous diet, 15% diluted in AMEn and nutrient content) and 2 vitamin C feed inclusions (0 vs. 200 mg/kg). At 6, 15, and 22 wk, blood sampling was carried out (4 birds/replicate) to determine serum alkaline phosphatase ( ALP ) levels, and behavior was observed by visual scan sampling. At 22 wk, carcass traits, tibia parameters, and intestinal morphology were assessed (2 birds/replicate), and tail- and wing-feather integrity of all birds were scored. Fibrous diet did not modify BW uniformity, mortality, or tibia growth when compared with control diet. Pullets fed the fibrous diet had lower tibia breaking strength, elastic modulus, and ash content values ( P < 0.05). They also had lower ALP serum level at 6 and 22 wk ( P < 0.05), their breast muscle was less developed (18.5 vs. 19.8%, P < 0.05), and their abdominal fat deposition was higher (1.14 vs. 0.87%, P < 0.05). At 15 and 22 wk, they performed, on average, 97% less grasping feather pecking and 45% less non–food object pecking behaviors, and their wing-feather score was lower ( P < 0.05) at 22 wk. Tail- and wing-feather scores of the control treatments were reduced by vitamin C inclusion (tail: 0.30 vs. 1.15, P < 0.05; wing: 0.98 vs. 1.26, P < 0.05) at 22 wk. In conclusion, fibrous diet improves carcass traits (reduces breast muscle and increases abdominal fat deposition), deteriorates bone mineral deposition and thus skeletal strength, and reduces stereotypic behaviors, improving wing-feather integrity. Vitamin C inclusion improves tail- and wing-feather integrity of lower in feed allowance.