- Unexpected steric effects of "remote" alkyl groups on the rate of conjugate additions to alkyl α,β-ethylenic sulfones, sulfoxides, and esters
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Examination of conjugated ethylenic sulfones, sulfoxides, and esters in Michael-type addition reactions reveals, for the first time, that the size of the heteroatom-attached alkyl group affects the rate of conjugate addition. Molecular modeling strongly suggests that what are generally considered to be "remote" alkyl groups in -CβH=CαHS(O) n,-alkyl systems and -CH2CβH=C αHCOO-alkyl systems are actually not remote from the β-carbon atom of the Michael accepting unit. Molecular modeling clearly shows that the alkyl groups in these Michael acceptors shield the β-carbons in the following order: Et i-Pr > t-Bu.
- Usera, Aimee R.,Posner, Gary H.
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p. 2329 - 2334
(2007/10/03)
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- On the reported intermediacy of vinyl radicals in spontaneous polymerization: An ESR-spin trapping study and its significance for the bond forming initiation theory
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Deuterated isopropyl vinyl sulfides and diethyl fumarate were synthesized and employed in a re-investigation of the mechanism of initiation of spontaneous polymerization of these comonomers by means of spin- trapping/ESR spectroscopy. Previous radical spin-trapping studies had been interpreted as indicating the involvement of vinyl radicals. While our studies produced data substantially in agreement with the previous study, it must be noted that the date are not consistent with literature data for other vinyl radicals. Accordingly, results from both spin-trapping/ESR studies me inconsistent with involvement of vinyl radical intermediates, but are consistent with initiation by tetramethylene diradicals.
- Mash, Eugene A.,Korth, Hans-Gert,DeMoss, Suzanne M.
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p. 15297 - 15320
(2007/10/03)
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- DIVINYL SULFOXIDE. REACTION OF DIVINYL SULFOXIDE WITH THIOLS
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The nucleophilic addition of thiols to divinyl sulfoxide was investigated.As a result β-(alkylthio)ethyl vinyl sulfoxides and di(β-alkylthioethyl) sulfoxides were obtained for the first time and characterized.At 220-320 deg C the β-(alkylthio)ethyl vinyl
- Trofimov, B. A.,Gusarova, M. K.,Efremova, G. G.,Amosova, S. V.,Kletsko, F. P.,et al.
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p. 2168 - 2172
(2007/10/02)
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