Resonance stabilized radicals features

Several other noteworthy features of resonance-stabilized radical thermochemistry are ... 

The most obvious feature of Pycnogenol, owing to the basic chemical structure of its components, is its strong antioxidant activity. Phenolic acids, polyphenols, and in particular flavonoids are composed of one (or more) aromatic rings bearing one or more hydroxyl groups and are therefore potentially able to quench free radicals by forming resonance-stabilized phenoxyl radicals. " The ability to quench the reactivity of... 

An Important feature of butene pyrolysis Is the existence of free radicals with resonant stabilization energy. The allyl and the 2-butenyl (methylallyl) radicals are stabilized by the fact that they have delocalized electrons. Added stability of these free radicals Is about 10 to 13 kcal/mole (16), which significantly increases the rate of their production and decreases the rate of their consumption. 

The key feature of this mechanism is that electron transfer between the photosensitizer and the dialkylphenacylsulfonium salt results in the generation of a cation-radical species which ultimately initiates polymerization. The co-product of the reaction is a resonance-stabilized sulfur radical species which eventually undergoes fragmentation as shown in Eq. (81). 

In polymerizing systems, the resonance-stabilised fragments could act mainly as terminating species, but it remains a fact nonetheless, that their formation, simultaneous with a reactive, initiating radical, is a general feature of the known, efficient, photoinitiator systems presumably because their relative stability facilitates dissociation. This may help to explain why benzil... 

We will not explore the computational details of VB theory, but it is worth noting some results that can be obtained with it. Recall that one of the features of HMO theory is that it is possible to make useful predictions, such as the relative stabilities of cyclic n systems or the locations of impaired electron density in a conjugated radical, without actually doing the HMO calculations. Similarly, it is not necessary to carry out a complete valence bond calculation to obtain useful quantitative predictions of resonance energies and some other properties of conjugated n systems. Herndon described a structure-resonance theory (SRT) method that enables one to calculate resonance energies using only Kekule structures The methods described in the references present... 

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