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Triplet oxygen cycloaddition with diradicals

Cycloaddition of triplet oxygen with diradicals and latent... [Pg.189]

Highly strained alkenes often behave chemically as 1,2-diradicals, and can therefore readily react with triplet oxygen (Scheme 3.6). 1,2-Quinodimethanes can also react as diradicals, and can undergo a formal [2 + 4] cycloaddition with triplet oxygen to yield cyclic peroxides (first example, Scheme 3.22). That this reaction also proceeds in the dark strongly indicates that no singlet oxygen is involved [87]. [Pg.51]

Oxidation of NSBVs 1 by oxygen resulted in oxidation of two C-H bonds and C-N bond cleavage. Formation of cycloaddition products 6-23 or 6-24 were not observed, demonstrating different oxidation reaction pattern of NSBVs from SB Vs. The possible mechanism for this oxidation process is given in Scheme 6.3. The triplet-state, diradical form 6-1 of NSBV 1 would react with oxygen to form a cycloaddition product 6-25. Homolysis of 0-0 bond leads to bis(oxy) diradical 6-26. Double abstraction of two a-H in bis(oxy) diradical 6-26 by oxygen and the... [Pg.150]

Some examples of photoadditions of carbonyl groups to ethylenic systems in solution are shown in Eqs. (64)-(66). In Reaction (65) the absence of quenching by oxygen in the vapor phase was taken to imply that this cycloaddition occurs from a singlet excited state. The stereospecificity of the reaction [Eejs. (64) and (66)] indicates that addition of excited ketone to the olefins occur s with formation of the most stable diradical (Hammond and Turro, 1963). If a triplet state were involved, cyclization would follow spin-flipping. [Pg.278]


See other pages where Triplet oxygen cycloaddition with diradicals is mentioned: [Pg.196]    [Pg.199]    [Pg.291]    [Pg.196]    [Pg.199]    [Pg.639]    [Pg.639]    [Pg.525]    [Pg.1060]    [Pg.220]    [Pg.1060]   
See also in sourсe #XX -- [ Pg.192 , Pg.193 , Pg.194 , Pg.195 , Pg.196 , Pg.197 , Pg.198 , Pg.199 , Pg.200 , Pg.201 , Pg.202 , Pg.203 ]




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