The thiolate anion as a nucleophile Part VIII. Reactions of dibromotetrafluorobenzenes

The reactions of the isomeric dibrometetrafluorobenzenes with the methanethiolate anion and copper(I) methanethiolate have been examined. Using the thiolate anion replacement of fluorine by the SMe group occurred, but with copper(I) methanethiolate protodebromination and replacement of the bromine with the SMe group occurred. The new compounds isolated have been characterized and their spectra (NMR, IR, and mass) examined.     

Reactions of some bromofluorobenzenes with copper(I) benzenethiolate

The reactions of copper(I) benzenethiolate with some bromofluorobenzenes have resulted in the replacement of the bromine by a phenylthio group. Combinations of this method and the reactions of sodium thiolates with fluorobenzenes have enabled various isomeric phenylthio substituted fluorobenzenes C₆H_xF_y(SR)_z to be prepared. The new products have been characterized by elemental analyses, mass, infrared, and fluorine NMR spectroscopy.     

Some reactions of copper(I) pentafluorothiophenolate as a nucleophile

Several aromatic compounds containing one or two C₆F₅S groups have been prepared by nucleophilic displacement reactions using CuSC₆F₅ in DMF solution. Aromatic iodine or bromine, rather than chlorine of fluorine is replaced by the SC₆F₅ group using CuSC₆F₅. A mechanism is postulated. New compounds prepared include $\text{p}$-(C₆F₆F₅S)₂C₆H₄, $\text{o}$- and $\text{m}$-(C₆F₅S)₂C₆F₄ and $\text{p}$XC₆H₄SC₆F₅(X=C1, NO₂, I, CH₃, CO₂C₂H₅).     

Study of the peak effect phenomenon in single crystals of 2H-NbSe2

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability effects and pinning.     

The thiolate anion as a nucleophile Part IV. Reactions of some pentafluorophenyl compounds

Direct nucleophilic substitution with sodium methanethiolate of the pentafluorophenyl compounds C₆F₅X (X = Cl, Br, I. NO₂, NH₂, CO₂H, SC₆F₅, OMe, OH) has given varying amounts of XC₆F₄(SMe), XC₆F₃(SMe)₂, C₆F₄(SMe)₂, XC₆F₂(SMe)₃ and C₆F₂(SMe)₄. In some cases cleavage of the aromatic carbon-X bond (X = Br, I, CO₂H, SC₆F₅) forming C₆F₄(SMe)H and C₆F₂(SMe)₃H, and the O-Me bond forming HOC₆F₂(SMe)₃ was observed. The new compounds isolated have been characterized by elemental analyses, infrared and mass spectra and their stereochemistries have been from their ¹H and ¹⁹F NMR spectra.     

Dichlorocarbene Addition to

In contrast to the terminal phosphinidene complex PhPW(CO)(5) (2), which adds to [5]metacyclophane (1) in a 1,4-fashion, dichlorocarbene preferentially adds in a 1,2-fashion to the formal "anti-Bredt" type double bond of the aromatic ring of 1 to afford the norcaradiene 11b, which immediately rearranges to the bridged cycloheptatriene 12b and further by a [1,5] sigmatropic chlorine migration to the isomeric 13b as the first observable product. More slowly, the latter isomerizes via a dissociative mechanism to give 15b. A computational study supports the notion that the [1,5] chlorine migration in the rearrangement 12b --> 13b, for which an activation barrier of 70.2 kJ mol(-)(1) was calculated, is essentially concerted with minor charge separation. In contrast, the analogous [1,5] chlorine migration in the flat model compound 7,7-dichlorocycloheptatriene (12a) displays features of a dissociative pathway.