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P-Fragmentation

The p-scission of a phosphoniumyl radical yields a cation and a phosphonyl radical, while its reaction with a nucleophile generates a phosphoranyl radical which can undergo SET reactions and a- or p-fragmentations (Scheme 14). [Pg.53]

During the last two decades, Bentrude et al. [70] has shown that phosphoranyl radicals exhibiting very slow a- and P-fragmentations react with alkyl disulfides via Sh2 homolytic substitution (Scheme 35) [70b]. The reactivity of phosphoranyl radicals in these Sh2 reactions depends strongly on the substituents attached to the phosphorus atom and on the structure of the disulfides [70c]. [Pg.63]

Phosphoranyl radicals can be involved [77] in RAFT processes [78] (reversible addition fragmentation transfer) used to control free radical polymerizations [79]. We have shown [77] that tetrathiophosphoric acid esters are able to afford controlled/living polymerizations when they are used as RAFT agents. This result can be explained by addition of polymer radicals to the P=S bond followed by the selective p-fragmentation of the ensuing phosphoranyl radicals to release the polymer chain and to regenerate the RAFT agent (Scheme 41). [Pg.66]

Maslak, P. Fragmentations by Photoinduced Electron Transfer. Fundamentals and Practical Aspects. 168, 1-46 (1993). [Pg.296]

Krauss, D. Mainx, H.G. Tauscher, B. Bischof, P. Fragmentation of Trimethyl-silyl Derivatives of 2-Alkoxyphenols a Further Violation of the Even-Electron Rule. Org. Mass Spectrom. 1985, 20, 614-618. [Pg.321]

Barros M, De Souza Silva MA, Huston JP, Tomaz C (2002) Anxiolytic-like effects of substance P fragment (SP(l-7)) in non-human primates (Callithrix penicillata). Peptides 23 967-973... [Pg.157]

The parent peak, usually having the highest m/e value, can easily be identified in all cases. Triphenyl-X -phosphorin also has an intense peak at m/e = 120, which Markl attributes to the C Hs-C = P fragment. Fig. 11 shows the mass spectra... [Pg.34]

Quantum yields, free energy changes, — AG°, for the electron transfer reaction from the P fragment to the Q fragment of P-L Q molecules in methylene chloride solution [55]... [Pg.333]

Cyclobutane derivatives can also be opened under reductive conditions. The reductive a,P-fragmentation of y-halocyclobutylketones (Eq. (19)) has been studied... [Pg.147]

The first complexes to contain the P=P fragment were synthesized in the metal coordination sphere. The parent diphosphene, HP=PH, is unknown in the free state, but is quite stable in (41).285... [Pg.1045]

ADDITIONS TO CARBON-NITROGEN AND CARBON-OXYGEN MULTIPLE BONDS, AND p-FRAGMENTATIONS... [Pg.815]

Water Elimination, Heterolytic P-Fragmentation and Formation of Radical Cations 118... [Pg.102]

Carbon-centered radicals may undergo homolytic P-fragmentation reactions, whereby an olefin and a new radical is formed. This reaction is, in fact, the reverse of the polymerization reaction. With neighboring C-C bonds, these P-frag-mentation reactions are usually slow, and only observable, at least on the pulse radiolysis time-scale with negatively-charged polymeric radicals whose lifetime is prolonged by electrostatic repulsion. Then, even the situation of equilibrium polymerization maybe approached (Ulanski et al. 2000 Chap. 9.4). [Pg.117]

Many O-centered radicals undergo facile P-fragmentation. For example, acyl-oxyl radicals which are intermediates in the electrolytic oxidation of acids (Kolbe electrolysis), rapidly decompose into alkyl radicals and C02 [reaction (1)]. The rate of these reactions is in the order of 109 s 1 and increases with increasing branching of the alkyl substituent, i.e., decreasing C-C02 bond energy (Table 7.1). [Pg.138]

Similarly, the p-fragmentation of tertiary alkoxyl radicals [reaction (2)] is a well-known process. Interestingly, this unimolecular decay is speeded up in a polar environment. For example, the decay of the ferf-butoxyl radical into acetone and a methyl radical proceeds in the gas phase at a rate of 103 s 1 (for kinetic details and quantum-mechanical calculations see Fittschen et al. 2000), increases with increasing solvent polarity (Walling and Wagner 1964), and in water it is faster than 106 s 1 (Gilbert et al. 1981 Table 7.2). [Pg.138]


See other pages where P-Fragmentation is mentioned: [Pg.434]    [Pg.53]    [Pg.130]    [Pg.366]    [Pg.35]    [Pg.548]    [Pg.146]    [Pg.110]    [Pg.821]    [Pg.860]    [Pg.41]    [Pg.312]    [Pg.238]    [Pg.238]    [Pg.248]    [Pg.253]    [Pg.23]    [Pg.329]    [Pg.358]    [Pg.779]    [Pg.102]    [Pg.103]    [Pg.117]    [Pg.136]    [Pg.139]   


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Heterolytic P-Fragmentation

P-Fragmentation Reactions

P-scission fragmentation

Rademacher, P., Fragmentations

Tandem P-fragmentation

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