107961-62-6Relevant articles and documents
Absolute Rate Expressions for Intramolecular Displacement Reactions of Primary Alkyl Radicals at Sulfur
Franz, James A.,Roberts, David H.,Ferris, Kim F.
, p. 2256 - 2262 (2007/10/02)
Arrhenius parameters are presented for the intramolecular displacement reactions of 4-(alkylthio)butyl radicals, where alkyl = benzyl, propyl, and tert-butyl, giving tetrahydrothiophene and the corresponding alkyl radical (R.).Arrhenius expressions were determined by competition of the rearrangement (displacement) with abstraction of hydrogen from tributylstannane.The Arrhenius parameters for the intermolecular displacement reactions were as follows ., log (A/s-1), Ea (kcal/mol), at the 95percent confidence interval>: benzyl, 9.92 +/- 0.22, 8.63 +/- 0.40; tert-butyl, 10.77 +/- 0.24, 11.36 +/- 0.40; n-propyl, 10.17 +/- 0.56, 12.15 +/- 1.16.The 4-(benzylthio)butyl and 4-(propylthio)butyl radicals undergo a competing intramolecular 1,6-hydrogen migration to form the corresponding α-(butylthio)benzyl and (butylthio)propyl radicals.The Arrhenius parameters -1), Ea (kcal/mol), 95percent confidence interval>, per hydrogen atom abstracted, for these latter two reactions were as follows: 4-(benzylthio)butyl,9.51 +/- 0.28, 8.87 +/- 0.44; 4-(propylthio)butyl, 9.10 +/- 1.9, 9.98 +/- 3.9.The Arrhenius parameters of the intramolecular displacement reaction are consistent with a product-like rate-determining step, as opposed to the formation of an intermediate sulfuranyl radical followed by nonselective ligands loss.INDO calculations predict the SOMO of the trialkylsulfuranyl radicals to be a ?* orbital with electron density distributed about sulfur and two pseupoapical carbons.The pseudoapical C-S-C angle defined by this SOMO suggests a predominance of exocyclic (axial-axial) displacement over endocyclic (equatorial-axial) displacement for the intramolecular displacement reactions forming a tetrahydrothiophene ring.MM2 calculations of internal rotational barriers of tert-butyl, hex-5-en-1-yl, and the 4-(alkylthio)butyl radicals and of the exocyclic ligands of models of the displacement transition structures are presented to aid in the interpretation of displacement A factors.
