Radical dialkylaminyl

Nitrogen- and oxygen-centered radicals offer some specific features. The rate constant of the reaction of dialkylaminyl radicals with (TMSlsSiFl is close to the analogous reaction of secondary alkyl radicals. In the reactions of... 

The reactions of t, -7, and singlet arenes (132) with dialkylamines in nonpolar solvents occur via the formation of the dialkylaminyl radical,, rather than the more stable... 

Cyclization of the aminyl radical 22 is slow and reversible [53], and the kinetics of related cyclizations and ff-fragmentations were measured directly by LFP [54]. Protonation of the dialkylaminyl radicals gives dialkylaminium cation radicals such as 24 that react much more rapidly [55], and Lewis acid complexes of aminyl radicals such as 23 are intermediate in reactivity [56]. Clocks such as 23 and 24 are in equilibrium with the neutral aminyl radicals, and the concentrations of the proto-nated or complexed forms are necessary if one is to use these clocks equilibrium constants for protonations and Lewis acid complexations in some solvents were determined in the initial kinetic calibration studies. 

Aminyl radicals are less reactive than carbon radicals, which in turn are less reactive than alkoxy radicals. For dialkylaminyl radicals, the reduction rate constant with tributyltin hydride 5 x 10 M s ) [14] is about ten times lower than for primary alkyl radicals [15] and a thousand times lower than for alkoxy radicals [16]. 

This reactivity pattern follows the X-H bond dissociation energies. Even though nitrogen is more electronegative than carbon, it forms weaker bonds to hydrogen. Similarly, for dialkylaminyl radical, the addition rate constants of 5-exo-trig cycli-... 

Thus, the types of reactions favored by amino radicals depend to a significant degree upon the extent with which the lone electron pair is associated with a proton, with a Lewis acid, or with an electron-withdrawing group. Clearly, aminium radical cations 2 (Scheme 1), metal-complexed aminyl radicals 3, amidyl radicals 4, sulfo-namidyl radicals 5 and cyanamidyl radicals 6 are electrophilic in nature. On the other hand, dialkylaminyl radicals 1 have been shown to display nucleophilic character... 

The sluggishness of the addition of neutral dialkylaminyl radicals to olefins, as well as their strong tendency towards non-selective abstraction of hydrogen, seemed to... 

Other reviews that have appeared this year include those on radical combination and disproportionation reactions, theoretical models for addition and abstraction reactions, homolytic addition reactions of dialkylaminyl radicals and the chemistry of nitroarene and aromatic A -oxide radicals. ... 

The reactions of - -t and 7 with secondary aliphatic amines are proposed to occur via formation of a nonfluorescent singlet ex-ciplex which yields a dialkylaminyl-l,2-diphenylethyl radical pair. The stereoselective formation of 69 indicates that radical pair combination is exclusively an in-cage process which competes effectively with rotation of the 1,2-diphenylcyclobutyl radical. The limiting quantum yields for the formation of 68 and 69 in nonpolar solvent are 0.14 and 0.16, respectively. Unlike the reaction of It with tertiary aliphatic amines, the quantum yield for the formation of 68 decreases with increasing solvent polarity (113). 

In reaction of aliphatic nitro compounds with alkyl radicals 6 7 generated from ethers or alcohols aminyloxides 69b could be detected79. Moreover dialkylaminyl-oxides 74b are formed, 67 being trapped from the corresponding nitroso compound. Reduction of nitro compound to nitroso compound probably occurs by electron transfer from alkyl radical 67 to nitro compound, subsequent dissociation of the resulting complex 68b giving nitro anion radical which finally disproportionates. 

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