Acetylene shape

Smirnov V. V., Fabelinskii V. I. Pressure-induced change of the shape and width of the coherent anti-Stokes light scattering spectrum of the V2 oscillations of acetylene. JETP Lett. 27, 123-5 (1978) [Pis ma ZhETP, 27, 131-4 (1978)]. 

Laser Doppler anemometry data showing the axial velocity along the centerline of a 380 mm long closed chamber during the formation of acetylene/air tulip flames of different equivalence ratios. The velocity is measured 265 mm from the ignition thus, the tulip shape is already formed before the flame reaches the measurement point. This work shows the behavior similar to the results described in Figure 5.3.9. (Adapted from Starke, R. and Roth, R, Combust. Flame, 66,249,1986.)... 

Abstract The past two decades have profoundly changed the view that we have of elemental carbon. The discovery of the fullerenes, spherically-shaped carbon molecules, has permanently altered the dogma that carbon can only exist in its two stable natural allotropes, graphite and diamond. The preparation of molecular and polymeric acetylenic carbon allotropes, as well as carbon-rich nanometer-sized structures, has opened up new avenues in fundamental and technological research at the interface of chemistry and the materials sciences. This article outlines some fascinating perspectives for the organic synthesis of carbon allotropes and their chemistry. Cyclo[n]carbons are the first rationally designed molecular carbon allotropes, and... 

Figure 1.6 Representative TEM image (a) and particle size distribution (b) obtained for a Au/Ti02 catalyst prepared by grafting of a [Au6(PPh3)6](BF4)2 complex onto Ti02 particles followed by appropriate reduction and oxidation treatments [42], The gold particles exhibit approximately spherical shapes and an average particle size of 4.7 nm.The measured Au particle sizes could be well correlated with the activity of the catalyst for carbon monoxide oxidation and acetylene hydrogenation. (Reproduced with permission from Springer.)...

The burner head itself is interesting. The flame must be wide (for a long pathlength), but does not have to be deep. In other words, the burner has a long slot cut in it (5 or 10 cm long) to shape the flame in a wide but shallow contour. Typically, the flame is 10 cm wide for air-acetylene and 5 cm wide for N20-acetylene. See Figure 9.9. 

A similar approach was taken by Moore [27], utilizing poly(phenyl acetylene) dendrimers with a dimethylbenzene moiety attached at the core of the dendrimer. An anomalous shift (41 nm) in the fluorescence spectra of the probe in various nonpolar hydrocarbon solvents was observed for G5 and G6, but not for G1 to G4. This observation confirmed significant in the size and shape changes for these dendrimers between G4 and G5. 

Different catalysts bring about different types of isomerization of hydrocarbons. Acids are the best known and most important catalysts bringing about isomerization through a carbocationic process. Brpnsted and Lewis acids, acidic solids, and superacids are used in different applications. Base-catalyzed isomerizations of hydrocarbons are less frequent, with mainly alkenes undergoing such transformations. Acetylenes and allenes are also interconverted in base-catalyzed reactions. Metals with dehydrogenating-hydrogenating activity usually supported on oxides are also used to bring about isomerizations. Zeolites with shape-selective characteristics... 

The primary particles of acetylene black have different shapes than those of other carbon blacks (Fig. 58). As the increased order in the c direction of the crystalline regions indicates, folded sheets of carbon layers are the main structural component. Their application is limited to special uses, e.g., in dry cells, because of their relatively high price. Total worldwide production is ca. 40 000 t/a. 

The thermal decomposition of 7, 8 and 9 into fullerenic substructures is a milestone in fullerene formation and represents the first example of a macroscopic preparation of closed-shell carbon particles from acetylenic precursors. However, molecular allotropes of carbon, such as Cgo or higher fullerenes were not found among the decomposition products. It is interesting to note in this context that 10 [24], a structural isomer of 7 with a saddle-shaped solid state conformation, also shows thermal transformations, but in this case they occur at temperatures ca. 50 °C lower than those of 7 and are accompanied by a release of 50 kj mol-1 more energy. Although an insoluble carbonaceous material is formed during this process, further details of its nature are currently not known. 

The obvious drawback of Mikkelsen s MPE model is the spherical shape of the cavity, making the calculations for extended systems such as peptide models or for oblong molecules such as acetylene rather awkward. This is improved in the IEF-PCM model, which is currently most often used to calculate solvent effects on the spin-spin coupling constants. 

---