Hydrocarbon clusters

Hydridotris(pyrazolyl)borates, as cobalt complex ligands, 44 274-278 Hydroboration, 16 230-234 chain lenghtening, 16 231-232 role in sythesis, 16 231, 232 Hydrocarbons clusters, 18 57-59... 

An alternative starting material for carbon fiber production is pitch—a complex mixture of fused polyaromatic hydrocarbon clusters that can also be melt-spun into fibers. 

In Table 4 there are presented data, concerning the specific adsorption of the ions at the silica/aqueous electrolyte interface. Metal ions may adsorb with formation of inner-sphere complexes, hydrocarbon clusters (for example Cu2+) or outer-spherical complexes as for example Mn2+ [105]. The determination of the adequate adsorption mechanism is possible with in situ spectroscopy method (Table 4). 

Exercise 4.2. What hydrocarbon cluster is analogous to Co4(CO)i2 Write the main-group and metal isolobal fragments. Write out the compositions and draw the structures of all the mixed Co/C clusters possible between these two homonuclear Co and C clusters. 

In the past 15 years, the synthesis of a series of 3-connected electron precise hydrocarbon clusters [CnHn]5 (see Fig. 2 for examples) has renewed interest in localised bonding schemes, since the bonding orbitals in these clusters are topologically equivalent to edge-localised 2 c-2 e bond pairs in a Valence Bond sense. Schulman et al. performed ab initio calculations on cubane [CgH8] utilising a basis set of 2c-2e localised C-C and C-H... 

Fig. 2. 3-connected geometries adopted by the hydrocarbon clusters [CnHn]... 

As mentioned in Sect. B, the bonding in 3-connected clusters, such as the hydrocarbon clusters [CnHn] depicted in Fig. 2, may be described in terms of 3n/2 (2c - 2e) bonds which are localised along the cluster edges. We have applied TSH theory to study these molecules, in an attempt to rationalise bonding differences between 3-connected and deltahedral clusters152. ... 

Low mass peaks (below w/z=60, C4, and smaller hydrocarbon clusters) are removed from the PCA calculation to exclude these hydrocarbon peaks that carry no specific chemical information. High mass peaks above m/z=500 are not included due to their low ion intensities. 

Kebarle P, Yamdagni R, Hiroaka JK and McMahon TB (1976) Ion molecule reactions at high pressure recent proton affinities, gas phase acidities and hydrocarbon clustering results. International Journal of Mass Spectrometry and Ion Physics 19 71-87. 

Os3(CO)ii(NCMe)] with azulene gave [Os3( i-H)2(ii3-p p p -CioH6)(CO)9] (97) 144 latter contains a terminal carbine-metal bond, the first carbenic hydrocarbon-cluster interaction in the absence of stabilising heteroatoms. 

Hot filament CVD. After the soot samples were collected, they were dissolved in benzene or carbon tetrachloride solvents and filtered. The solutions were then used for the mass analysis or UV-vis measurements. Some raw soot was analyzed directly by mass spectrometry. A time-of-flight mass spectrum of the soot solution is shown in Fig. 3 both Ceo and C70 peaks are present. For pressure variations between 30 to 100 torr, the samples also showed the fiillerene peaks 18). In an attempt to increase the yield of soot, we increased the methane concentration to 2% and lowered the filament temperature to about 1700°C. Under these conditions, no diamond was formed and we were able to increase the soot yield by a factor of 6 to about 100 mg per run. However, no fiillerene formed, only hydrocarbon clusters. 

Figure Bl.19.13. (a) Tliree STM images of a Pt(l 11) surface covered witli hydrocarbon species generated by exposure to propene. Images taken in constant-height mode. (A) after adsorption at room temperature. The propylidyne (=C-CH2-CH2) species that fomied was too mobile on the surface to be visible. The surface looks similar to that of the clean surface. Terraces ( 10 mn wide) and monatomic steps are the only visible features. (B) After heating the adsorbed propylidyne to 550 K, clusters fonn by polymerization of the C H...

The reactivity of size-selected transition-metal cluster ions has been studied witli various types of mass spectrometric teclmiques [1 ]. Fourier-transfonn ion cyclotron resonance (FT-ICR) is a particularly powerful teclmique in which a cluster ion can be stored and cooled before experimentation. Thus, multiple reaction steps can be followed in FT-ICR, in addition to its high sensitivity and mass resolution. Many chemical reaction studies of transition-metal clusters witli simple reactants and hydrocarbons have been carried out using FT-ICR [49, 58]. 

To explain how solid acids such as Nafion-H or HZSM-5 can show remarkable catalytic activity in hydrocarbon transformations, the nature of activation at the acidie sites of such solid acids must be eon-sidered. Nafion-H contains acidic -SO3H groups in clustered pockets. In the acidic zeolite H-ZSM-5 the active Bronsted and Tewis acid sites are in close proximity (—2.5 A). 

Lipid bilayer (Section 26 4) Arrangement of two layers of phospholipids that constitutes cell membranes The polar termini are located at the inner and outer membrane-water interfaces and the lipophilic hydrocarbon tails cluster on the inside... 

In the discussion of the relative acidity of carboxylic acids in Chapter 1, the thermodynamic acidity, expressed as the acid dissociation constant, was taken as the measure of acidity. It is straightforward to determine dissociation constants of such adds in aqueous solution by measurement of the titration curve with a pH-sensitive electrode (pH meter). Determination of the acidity of carbon acids is more difficult. Because most are very weak acids, very strong bases are required to cause deprotonation. Water and alcohols are far more acidic than most hydrocarbons and are unsuitable solvents for generation of hydrocarbon anions. Any strong base will deprotonate the solvent rather than the hydrocarbon. For synthetic purposes, aprotic solvents such as ether, tetrahydrofuran (THF), and dimethoxyethane (DME) are used, but for equilibrium measurements solvents that promote dissociation of ion pairs and ion clusters are preferred. Weakly acidic solvents such as DMSO and cyclohexylamine are used in the preparation of strongly basic carbanions. The high polarity and cation-solvating ability of DMSO facilitate dissociation... 

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