The effects of central atom and apical atom electronegativity on the reactions of novel sulfur and selenium hypervalent species
Rongione, Joseph Charles
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https://hdl.handle.net/2142/22903
Description
Title
The effects of central atom and apical atom electronegativity on the reactions of novel sulfur and selenium hypervalent species
Author(s)
Rongione, Joseph Charles
Issue Date
1991
Doctoral Committee Chair(s)
Martin, J.C.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Language
eng
Abstract
Solutions of 10-S-5 methylsulfurane oxides in CD$\sb3$OD undergo deuterium exchange at the equatorial S-CH$\sb3$. The rate of deuteration for the CH$\sb3$-substituted methylsulfurane oxide is 86,000 times faster than for the CF$\sb3$-substituted methylsulfurane oxide. Both anions are shown by NMR to be unsymmetrical 8-S-4 species, formed by cleavage of one of the apical S-O bonds. Reduction of the acidity by replacement of CH$\sb3$ by CF$\sb3$ results from the greater negative charge on the two apical oxygens of the neutral hypervalent species. The total negative charge on the two oxygens is reduced upon forming the unsymmetrical 8-S-4 species, although these are anions.
The CH$\sb3$-substituted methylsulfurane oxide is methylated at an apical oxygen yielding the first example of an O-alkylated sulfone cation that is unreactive towards water either as a crystalline solid or in solutions. The X-ray crystallographic structure obtained is the first one for an O-substituted sulfone. The steric bulk of the benzyldimethylmethoxy group ortho to the O-alkylated sulfone and opposite to the alkylated oxygen, is believed to be protecting the cationic sulfur site from direct nucleophilic attack opposite to the OR group of the sulfur, thus stabilizing the O-alkylated sulfone.
The methylation of pyridine-$d\sb5$ is examined for a series of hypervalent sulfur compounds and rearranged sulfur species. These reactions are compared with the methylation of C$\sb5$D$\sb5$N by a family of isomeric sulfur species. An equatorial methyl group of the sulfurane oxide ($k\sb{\rm 25\sp\circ C}$ = 6.25 $\times$ 10$\sp{-6}$ s$\sp{-5}$), the equatorial methoxy group of the sulfurane ($k\sb{\rm 25\sp\circ C}$ = 1.06 $\times$ 10$\sp{-2}$ s$\sp{-1}$) and the 1-aryl-1-trifluoro-2,2,2-trifluoroethyl methyl ether with an ortho-sultine group ($k\sb{\rm 25\sp\circ C}$ = 2.26 $\times$ 10$\sp{-7}$ s$\sp{-1}$). Each forms a N-methylpyridinium sulfuranide oxide anion.
The synthesis and reactions of a novel series of hypervalent selenium species are reported. The more electropositive selenium (relative to sulfur) central atom, with a partial positive charge developed on the central atom, provides stabilization for the symmetrical 3-center 4-electron (3c-4e) bond more than for the isomeric unsymmetrical geometry, relative to sulfur. The longer Se-O bond lengths reduces the interaction between filled p-orbitals of the equatorial oxygens and antiboding orbital of the O-Se-O 3c-4e bond.
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