Radicals eliminations from

Stereoselective preparation of CEi-allyl alcohols via radical elimination from ruin -y-phenylthio-fi-nkro alcohols has been reported. The requisiteruin -fi-nitro sulfides are prepared by protonadon of nitronates at low temperanire Isee Chapter 4, and subsequent treatment v/ith Bu-vSnH induces and eliminadon to givelE -alkenes selecdvely IseeEq. 7.112. Unfortunately, it is difficult to get the pure syu-fi-nitro sulfides. Treatment of a rruxnire of syu- and ruin -fi-nitrosulfides v/ith Bu- SnH results in formadon of a rruxnire of (Ey and lZ -alkenes. 

Hydrogen Radical Elimination from Ionized Ethylene... 

Schwarz, H. Some Newer Aspects of Mass Spectrometric Ortho Effects. 73, 231-263 (1978). Schwarz, H. Radical Eliminations From Gaseous Cation Radicals Via Multistep Pathways — The Concept of Hidden Hydrogen Rearrangements, 97, 1-31 (1981). 

Stereoselective preparation of ( )-allyl alcohols via radical elimination from anti-j-phenylthio-P-nitro alcohols has been reported.154 The requisite anti-P-nitro sulfides are prepared by protonation of nitronates at low temperature (see Chapter 4), and subsequent treatment with Bu3SnH induces anti elimination to give (E)-alkenes selectively (see Eq. 7.112). Unfortunately, it is difficult to get the pure yyw-P-nitro sulfides. Treatment of a mixture of syn- and anti-P-nitrosulfides with Bu3SnH results in formation of a mixture of (E)- and (Z)-alkenes. 

Ono and coworkers have devised a new acetylene equivalent for the Diels-Alder reaction namely, l-phenylsulfony-2-nitroethylene is a very reactive dienophile, and the radical elimination from the adduct gives the Diels-Alder adduct of acetylene, as exemplified in Eq. 7.113. Other acetylene equivalents are summarized in a review.156... 

In coumarins which bear large alkyl side chains, such as osthol (122), the primary fragmentation does not involve carbon monoxide loss. The dominant processes are side chain cleavage, methyl radical elimination from the side chain, and loss of a methoxyl radical. The mass spectra of this and related naturally occurring coumarins have been intensively studied and reviewed (75RCR603). 

As with the simple alkylcoumarins, phenylcoumarins readily eliminate carbon monoxide from the molecular ion. Mass spectral fragmentation of 4-phenylcoumarin follows the route given in Scheme 10. The molecular ion (122a) appears as the base peak. Formyl radical elimination from (122b) produces the fluorenyl cation (122c), m/e 165 (63TL891). 

There may, however, be certain experimental conditions for which radical concentrations may be considered to be uniform throughout the reaction vessel. These would be mainly (a) low intensity so that the rate of reaction (19) is small and (b) either a low steric factor or ahigh activation energy for reaction (15). Under such experimental conditions radicals could diffuse far from points of formation. Unfortunately, these conditions will also permit numerous collisions between radicals and walls. If accommodation coefficients are high, so that wall collisions are effective in radical elimination from the system, the concentrations of radicals throughout the vessel may still be far from uniform10-12. 

Fig. 12. Schematic representation of CHJ and S radical elimination from the methamidophos compound. The numbers in parentheses indicate the masses of the different ions, which permitted their identification [reprinted with permission from Thompson et al. 24) copyright 1990 American Chemical Society].

The bimolecular rate constant for the condensation reaction 13 1 low relative to the rate constant for collision between C.F and C2F. Approximately one collision In fifty leads to the formation of products different from the reactants. In the discussion below of condensation reactions In partially fluorl-nated ethylenes, it will be shown that the rearrangement j whlch Is necessary for methyl radical elimination from a C (H,F)g complex is substantially Inhibited by the presence of F-atoms In the complex. This would explain the fact that the rate constants of these reaction are considerably lower, and also more dependent on the Internal energy content of the reactants as compared to the C2H - C2H reaction pair (, ]J). 

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