Stabilization of oxidized sulfur centers in organic sulfides. Radical cations and odd-electron sulfur-sulfur bonds

Abstract

If this interpretation is correct, the variable transition-state theory seems to be valid also for dehalogenation reactions. With meso-1,2-dibromo-1,2-diphenylethane as the substrate, the transition-state structure is central when the nucleophile is a halide ion and shifts toward the Elcb-like side with Ph3P. It is possible that with the latter base the incipient positive charge on the phosphorus atom in the transition state favors the buildup of negative charge a t Cg, thus promoting a transition state with carbanion character.The factors affecting base reactivity in dehalogenation reactions have been primarily investigated using the reactions of erythro-l-chloro-2-iodo-1,2-diphenylethane (eq 1, X = I, Y = Cl).61 The base attacks the iodine atom in this case, and elimination of IC1 takes place. The main conclusion of this study is that polarizability and desolvation energy are by far more important factors than basicity in determinating the reactivity of a base in a dehalogenation process. In particular, the role of polarizability is clearly shown by the reactivity order I-> Br-> C1-observed in dipolar aprotic solvent in both the reactions of erythro-lchloro-2-iodo-1,2-diphenylethane and meso-1,2-dibromo-1,2-diphenylethane. Concluding RemarksThe above discussion has shown that, despite the fact that quantitative work in this area has started only (61) E. Baciocchi and C. Lillocci, J . Chem. Soc., Perkin Trans. 2, 802 (1975). recently, some important conclusions regarding the influence of the base on the E2 transition state have been reached. This appears to be particularly true when the effects of basicity are considered. Little doubt now exists that, at least in anti eliminations, the stronger base generally produces a transition state with higher carbanion character. Confirmation of this conclusion in the case of syn eliminations is highly desirable.62Additional work on the effects of base associations appears to be necessary in light of the somewhat contradictory results obtained so far. Moreover, the effects of the steric requirements of the base should be further investigated. Also of great interest would be studies aimed at determining (through a-carbon and leaving group isotope effects) the influence of the base nature on the extent to which the bond between a-carbon and leaving group is weakened in the transition state. Such information would complement that given by p and kH/kD values, thus allowing a complete picture of the transition-state structure to be obtained. Z wish to acknowledge support by the Italian National Research Council (C.N.R.) and the contribution of m y co-workers whose names appear in the cited literature. I wish also to thank Professors R. A. Bartsch and D. J . McLennan for helpful comments. (62) Unpublished results from this laboratory have however shown that in syn eliminations from 12 promoted by phenoxides in Mez §O change in base strength does not significantly influence the carbanion character of the transition state.Organic sulfur compounds, among them sulfides, are kno...

Gas-phase scrambling of disulfide bonds during matrix-assisted laser desorption/ionization mass spectrometry analysis

“…It is known that radicals can undergo very fast intramolecular rearrangement reactions, particularly if structural and spatial conditions are favorable [26]. The tendency of the polarizable sulfur atom to participate in radical reactions has been known for decades in many fields of chemistry [27][28][29][30]. It has been demonstrated that electron attachment to a disulfide bond leads to significant bond weakening and formation of stable radical species at low temperature in solution [31,32].…”

Isolation and reversible dimerization of a selenium–selenium three-electron σ-bond

“…Odd-electron bonding is of both fundamental and practical interest [8][9][10][11][12][13] . Three-electron s-bonding was first proposed by Linus Pauling in 1931 (ref.…”

Access to Stable Metalloradical Cations with Unsupported and Isomeric Metal–Metal Hemi‐Bonds

“…Thelong Co-Co bonds in 1C + , 2C + ,and anti-3C + may be rationalized by as imple three-electron bonding model as formed by the interaction of am ono-cobalt radical cation center with lone pair electrons of another cobalt atom, leading to ab ond order of 1/2 or less,a nalogues to threeelectron s-bonds ( Figure S10) of main group elements. [10,17,18] To the best of our knowledge, 2C…”