Density of cyclohexane

Before we can apply our model, we have to assign values to the parameters x in Equation 2 and r and 1 in Equation 4. The quantity x is simply defined as pQM/ppM0, where pQ and p are the densities of cyclohexane and PS, respectively, and Mq ana M their respective moleculair weights. The choice for r and 1 is less... 

Figure 40 12. Pressure effect on liquid density of cyclohexane from - 38flC to - 236 C,...

The density of cyclohexane has been measured from its melting point to the critical point.1 13Figure 40 12 presents the data of Reamer and Sage on the effect of pressure on the density or cyclohexane.1 Data on the other three compounds arc available up to the boiling... 

As in example 2.3, we picture the liquid as being composed of cubic molecules. The size of each cube was calculated from the density of cyclohexane to be a = 0.565 nm. In the bulk each molecule is supposed to directly interact with 6 neighbors. The energy per bond is thus AvapU/6Na- At the rim two bonds less can be formed and the energy loss per molecule is 2AvapU / Na- Thus the energy difference per unit length is... 

Figure 16.9 Surfaces corresponding to the indicated value for the electron density of cyclohexane...

Calculate the liquid density of cyclohexane at the normal boiling point Tb = 353.85 K, P = 1 atm) with the help of the PR equation of state. 

Preparative electrochemical reduction of aryltrimethylsilanes in methyl-amine in the presence of LiCl gives the Birch-type products, 1,4-cyclohexan-dienes (Scheme 34) [6], A mechanism involving the electrochemical formation of lithium metal which chemically reduces the substrate has been suggested. The hydrogen atom is introduced on the carbon adjacent to the silicon preferentially. This regioselectivity is consistent with the spin density of the anion radical determined by ESR spectroscopy (Sect. 2.2.1). 

Fig. 36. Density of epoxy networks prepared via CIPS with cyclohexane before and after the drying procedure...

Fig. 56. Density of solvent-modified and macroporous cyanurates prepared with various amounts of cyclohexane via CIPS...

The dielectric constant of the pure cyanurate network under dry nitrogen atmosphere at 20 °C is 3.0 (at 1 MHz). For the macroporous cyanurate networks, the dielectric constant decreases with the porosity as shown in Fig. 57, where the solid and dotted lines represent experimental dielectric results together with the prediction of the dielectric constant from Maxwell-Garnett theory (MGT) [189]. The small discrepancies between experimental results and MGT might be due to the error in estimated porosities, which are calculated from the density of the matrix material and cyclohexane assuming that the entire amount of cyclohexane is involved in the phase separation. It is supposed that a small level of miscibility after phase separation would result in closer agreement of dielectric constants measured and predicted. Dielectric constant values as low as 2.5 are measured for macroporous cyanurates prepared with 20 wt % cyclohexane. 

Since the hydrogenolysis of cyclohexane and cyclohexane derivatives is less probable than the thermodynamically favored dehydrogenation to form aromatic compounds, most studies address hydrogenolysis only in connection with aromati-zation as an unwanted side reaction. An interesting observation by Somorjai showed, however, that hydrogenolysis of cyclohexane to form n-hexane becomes competitive with aromatization on Pt single crystals with increasing kink density.302 On a Pt surface where approximately 30% of the atoms in the steps are in kink positions, benzene and n-hexane are formed in 1 1 ratio. 

Figure 2 shows a multiple-echo, intensity-weighted cyclohexane MRM image of a 300 pm cross-sectional slice of a 4 mm diameter coke bean. The density-weighted H images are collected with an unprocessed image resolution of 24 pm pixel"1. Since the coke is packed in wet gypsum, the area outside the coke shows very little cyclohexane intensity and appears black. Several feature arise from this image which complement the SEM images in Figure 1. Firstly, a dark band at the perimeter of the coke corresponds to the exterior shell depicted in deal in Figure lc. This dark feature reflects the absence of cyclohexane and thus indicates the...

Fig. 21. (a) Cyclohexane dehydrogenation to benzene (O) and hydrogenolysis to n-hexane (A) as a function of step density, (b) Cyclohexane dehydrogenation to benzene and hydrogenolysis to n-hexane as a function of kink density at a constant step density of 2.0 x 1014/cm2. 

We have been able to identify another active site by studying the ratio of the dehydrogenation rate to hydrogenolysis rate of cyclohexane to benzene and /i-hexane, respectively (36a). While the benzene /j-hexane ratio is 3 1 on a stepped surface (with roughly 17% of the surface atoms in step positions), the ratio decreases rapidly with increasing kink density (Fig. 21b). Using a set of catalyst surfaces that were cut to maintain the same terrace width (step density equal to 2.5 x 1014/cm2), but with variable kink density in the steps, we have found that the hydrogenolysis rate increases linearly with kink... 

We have been able to identify two types of structural features of platinum surfaces that influence the catalytic surface reactions (a) atomic steps and kinks, i.e., sites of low metal coordination number, and (b) carbonaceous overlayers, ordered or disordered. The surface reaction may be sensitive to both or just one of these structural features or it may be totally insensitive to the surface structure, The dehydrogenation of cyclohexane to cyclohexene appears to be a structure-insensitive reaction. It takes place even on the Pt(l 11) crystal face, which has a very low density of steps, and proceeds even in the presence of a disordered overlayer. The dehydrogenation of cyclohexene to benzene is very structure sensitive. It requires the presence of atomic steps [i.e., does not occur on the Pt(l 11) crystal face] and an ordered overlayer (it is poisoned by disorder). Others have found the dehydrogenation of cyclohexane to benzene to be structure insensitive (42, 43) on dispersed-metal catalysts. On our catalyst, surfaces that contain steps, this is also true, but on the Pt(lll) catalyst surface, benzene formation is much slower. Dispersed particles of any size will always contain many steplike atoms of low coordination, and therefore the reaction will display structure insensitivity. Based on our findings, we may write a mechanism for these reactions by identifying the sequence of reaction steps ... 

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