0 VCH Verlagsgesellschaji mbH, 0-69451 Weinheim, 1997 0570-0833/97/3607-1603 $17.50 + SO/O 1603 B s ~~ COMMUNICATIONS Anxebr. Chm. Ini. E d Engl 1997. 36, No. 15 f ; VCH Verlagsgesellschaft mbH, D-69451 Weinhelm. 1997 0570-0833/97!3615-1607$ 17.50+ XI 0 CSJ2 d/quantitative yield.

No abstract

The synthesis of 13 trans-dimethyldihydropyrenes (bridged [ 14lannulenes) fused to one or more benzene, naphthalene, phenanthrene, phenalene, or quinoxaline rings and 6 cis-dihydropyrene derivatives from benzenoid precursors using either a thiacyclophane route or an electrocyclic addition of a furan to an annulyne followed by deoxygenation is reported. Their 'H NMR spectra are studied in detail to obtain correlations between 3 J~,~ coupling constants and the intemal methyl proton chemical shifts and also between the latter and the more distant external annulene ring proton shifts. These linear correlations are then used to obtain a relationship between the relative aromaticity of benzene and the fused ring in question, such that the aromaticity of the fused ring can be estimated relative to that of a benzene ring simply from a measurement of chemical shift in the fused annulene.

At the limits of analytical investigation one finds the nanodimensional C60 graphite segment 1, which, thanks to its long‐chain alkyl substituents, is soluble. Monolayers of 1 on graphite can be characterized by scanning tunneling microscopy.

No abstract

Carbon nanotubes (CNTs) have generated a tremendous amount of research interest because of their unique structural, electronic, magnetic, and mechanical properties. [1] Among the various synthetic methods employed for their preparation, chemical vapor deposition (CVD) has emerged to be most effective, and efforts are increasing in applying this technique to pre-growth device fabrication by utilizing (in particular lithographically) [2] patterned catalyst arrays and in situ tube assembly. [2,3] Crucial in this endeavor is the sitespecific batch production of ordered carbon with control of stoichiometry and ultimately morphology. One possible approach to achieving this would be the efficient thermal conversion of a defined, soluble, molecular organometallic precursor composed of both the carbon source and the metal catalyst, placed locospecifically by wetting and drying. Such a strategy would combine the advantages of the floating organometallic catalyst (for example, ferrocene, [Fe(CO) 5 ], etc.) CVD methodology [1d, 4] with a solid-state conversion of carbon precursors. Reports of the latter reveal some serious shortcomings with respect to yield and/or degree of graphitization, extremity of conditions, need for specialized equipment, the requirement of co-reagents, and simplicity of starting materials. [1d, 5] We have described the solid-state thermolysis of a [Co 2 (CO) 6 ]-complexed tetrabenzodehydro [20]annulene and some of its substructures to form ordered carbon material, but this method shared some of these drawbacks, in as much as the highest yields were only about 60 %. The desired product consisted of an (at best) approximately equal mixture of multiwalled tubes (MWNTs)

Furan adducts, 13, 15, and 16, of dimethyldihydropyrene are prepared in order to test the postulate that bicyclic annelations are generally effective at inducing bond localization in aromatic systems. A large 2-ppm downfield shift of the 1 H NMR shifts of the internal methyl signals in 15 compared to 16 provides a significant indicator of bond localization in 15. X-ray diffraction analysis of 13 displays regular bond length alternation. Ab initio computations that do not include dynamic electron correlation are found to be inadequate for modeling the molecular structure of 1. Density Functional Theory models 1 well and predicts bond localization in derivatives of 1 consistent with the observed NMR spectroscopic and X-ray diffraction results.

An die Grenzen der Analytik stößt man bei dem nanodimensionalen C60‐Graphitsegment 1, das dank langkettiger Alkylsubstitution löslich ist und dessen Monolagen auf Graphit durch Rastertunnelmikroskopie charakterisiert werden können.