Formation of the corannulene core by nickel-mediated intramolecular coupling of benzyl and benzylidene bromides: a versatile synthesis of dimethyl 1,2-corannulene dicarboxylate

[reaction: see text] A practical synthesis of dimethyl 1,2-corannulene dicarboxylate (5) is reported, with the final ring-forming step achieved by the double intramolecular nickel powder mediated coupling of benzyl and benzylidene bromide groups with 60% isolated yield.     

Shallow arch model. An asymptotic approach

We examine an asymptotic expansion of the time dependent displacement field of a solid, three-dimensional elastic arch. We show that it is possible to derive from the principles of virtual work four different models of arches. We also show that the approximate equations of motion are universal within a class of homogeneous, hyperelastic materials provided that the deformations of the solid arch are not too large.     

On the global geometry of the stephani universe

A preliminary investigation of global properties of the Stephani solution of the Einstein field equations is presented. This solution generalizes those of Friedman-Robertson-Walker (FRW) in such a way that the spatial curvature indexk (a constant in the FRW models) is a function of the time coordinate. The de Sitter solution, which is also a special case of the Stephani solution, is analyzed in the Stephani coordinates to gain insight into the global structure of the manifold and its foliation. The general metric is found to have several properties in common with this example. It has singularities which can be avoided either by matching the solution to an (as yet unknown) empty-space solution or confining the curvature index to be positive at all times.     

Anisochronism of large geminal groups in the 1H and 13C nuclear magnetic resonance spectra

The role of steric factors in magnetic non-equivalence anisochronism of complex geminal groups and of their fragments in compounds of the general formula RCH(Ph)CH(COOR′)₂ has been investigated. CMR anisochronism is more sensitive to conformational and other steric changes than is PMR.     

New evidence of the intrinsic chemical shift non-equivalence

Carbinols of the general formulae R·CHOH·C(NO₂)Me₂ exhibit increasing values of chemical shift non-equivalence for the geminal methyl groups with rise of temperature. This phenomenon furnishes indirect evidence for the intrinsic non-equivalence.     

Use of silver trifluoroacetate together with lanthanide shift reagents for simplification of 1H NMR spectra of aromatic hydrocarbons

The equimolar mixtures of typical lanthanide shift reagents such as Eu(fod)₃, Pr(fod)₃ or Yb(fod)₃ with silver trifluoroacetate, previously used to induce paramagnetic shifts in the ¹H NMR spectra of alkenes, have been successfully applied to simple aromatic hydrocarbons such as benzene, toluene, ethylbenzene and xylenes. In benzene and p-xylene the signals of all the aromatic protons are shifted identically. In other substituted benzenes the magnitude of the induced shift depends on the distance between the proton and the substituents. In addition, the different behaviour of the signals of the methyl groups in meta-and para-xylene on the addition of the complex shift reagent allows the quantitative analysis of the two xylenes in their mixtures.     

General dynamic theory of macromolecular networks. II. Dynamics of network deformation

On the basis of the general concepts of a macromolecular network as defined in the preceding paper, a detailed analysis of forces acting on a network chain is given. In all types of networks the chain tension involves elastic, diffusional, contact friction and internal viscosity terms; in entanglement networks there appears also an additional term associated with chain–chain friction at entanglement junctions. The force balance equation for a tetrafunctional network junction is derived. It is shown that exact formulation of this equation requires knowledge of the simultaneous configurations of all the network chains in the system. For energetic networks, solution of the force balance equation is not required for the determination of the distribution function; and the dynamics of such networks can be discussed in terms of a distribution function for a single chain. On the other hand, for entanglement and contact networks, where the force balance equation is a source of information about sliding rates, some simplified equations can be formulated and solved, by using a 4(N + 1)-dimensional distribution function for a single macromolecule with N network junctions. It is shown that for both network classes with nonlocalized junctions the position of a network chain within the macromolecule plays an essential role and is a source of the effects of molecular weight on the physical behavior of the system. The analysis of forces acting on a network chain reveals also some essential differences in the dynamic behavior of energetic, entanglement and contact networks and thus confirms the significance of the classification proposed in the preceding paper.