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Dissociative stereoisomerization of persulfuranes via 10-S-5 persulfonium salts. Geometrical isomers of octahedral 12-S-6 species

Journal Article · · J. Am. Chem. Soc.; (United States)
DOI:https://doi.org/10.1021/ja00370a039· OSTI ID:6739502
The reaction of bromine trifluoride with sulfurane gives rise to the first reported isolation of geometrical isomers of 12-S-6 sulfur, the trans- and cis-difluorodialkoxydiarylpersulfuranes. The cis isomer is 1.6 +/- 0.1 kcal/mol more favored in free energy than the all-trans isomer in methylene chloride solution at 25/sup 0/C. Calorimetry showed trans-to-cis isomerization to be exothermic by 2.0 +/- 0.5 kcal/mol. The rapid, acid-catalyzed isomerization of trans isomer to give cis isomer occurs by a dissociative mechanism through a pentacoordinate cationic sulfur intermediate, a 10-S-5 persulfonium ion, which was isolated at its hexafluorophosphate salt. A lower limit for the activation barrier of the unobserved nondissociative isomerization of trans to cis is 50 kcal/mol in quinoline solution. Polarization and other effects on the relative bond lengths and energies of the isomers are discussed. The results of complete X-ray structure determinations for trans and cis are described together with a PMO argument rationalizing the observed order of bond lengths.
Research Organization:
Univ. of Illinois, Urbana
OSTI ID:
6739502
Journal Information:
J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 104:6; ISSN JACSA
Country of Publication:
United States
Language:
English