Benzene with curved surfaces

The authors repeated the experiment with two, more strongly retained, solutes m-dimethoxy benzene and benzyl acetate. These solutes were found to elute at (k ) values of 10.5 and 27.0 respectively on a silica column operated with the same mobile phase. The results obtained are shown as similar curves in Figure 13. The m dimethoxy benzene, which eluted at a (k ) of 10.5, also failed to displace any ethyl acetate from the silica gel even when more than 0.5 g of solute resided on the silica surface. Consequently, the m-dimethoxy benzene must have also interacted with the surface by a sorption process. 

This formula is consistent with the fact that in stable equilibrium the energy of the surface must be a minimum for a given value of bubble or drop volume, and a sphere has the least surface area for a given volume. For general curved surfaces the radius a in Eq. (10.1.6) is frequently taken to be the mean radius of curvature defined as half the sum of the inverse principal radii of curvature. For immiscible liquids a refers to the interfacial tension, which, for example, for benzene over water at 20°C is 35mNm. Obviously for a plane interface, where the mean radius tends to infinity, the pressure difference will be zero. 

Figure 47. Surface phonon dispersion for CsHg/RhClll). The phonon dispersion curve of the benzene frustrated translational mode appears to have an avoided crossing with the RW of the Rh(lll) surface, similar to that of Kr/Pt(lll) in Fig. 44a, The orientation of the benzene on the surface (top and side views) is shown in the inset. (Reproduced from Fig. 8 of Ref. 130, with permission.)...

Isoxazole dissolves in approximately six volumes of water at ordinary temperature and gives an azeotropic mixture, b.p. 88.5 °C. From surface tension and density measurements of isoxazole and its methyl derivatives, isoxazoles with an unsubstituted 3-position behave differently from their isomers. The solubility curves in water for the same compounds also show characteristic differences in connection with the presence of a substituent in the 3-position (62HC(17)1, p. 178). These results have been interpreted in terms of an enhanced capacity for intermolecular association with 3-unsubstituted isoxazoles as represented by (9). Cryoscopic measurements in benzene support this hypothesis and establish the following order for the associative capacity of isoxazoles isoxazole, 5-Me, 4-Me, 4,5-(Me)2 3-Me> 3,4-(Me)2 3,5-(Me)2 and 3,4,5-(Me)3 isoxazole are practically devoid of associative capacity. 

More easily to be understood are the effects observed when ir electrons are present in the adsorbed molecule. Figure 28 shows the change of the photoelectric emission of a platinum surface covered with benzene (76). The benzene was contained in a capsule, which could be smashed magnetically (see F in Fig. 2). The tube, G in Fig. 2, was cooled by liquid air. At the points of the curve marked with arrows, the cooling of G was interrupted for 1 or 2 min., so that a small quantity of benzene molecules might be adsorbed at the platinum surface. The sensitivity increased (Fig. 28) at first and then decreased after passing a maximum, which was reached in the vicinity of the monomolecular covering (B, C in Fig. 28). 

The vibrational spectrum of benzene around 1000 cnf has also been measured. IQ. Benzene was physisorbed on a cooled copper substrate in the vacuum chamber. Figure 19 shows the transmission for several thicknesses of benzene and a prism separation of 3 cm. The thickness was determined from the measured transmission in transparent regions using Eg. (7). The solid curves were calculated from Eqs. (5) and (6) using optical constants for benzene obtained from an ordinary transmission experiment.il The benzene film was assumed to be isotropic. Of the two absorption lines seen, one belongs to an in-plane vibrational mode, and one to an out-of-plane vibration. Since the electric field of the SEW is primarily perpendicular to the surface, the benzene molecules are clearly not all parallel or all perpendicular to the copper surface. Also it should be noted that the frequencies are the same (within the experimental resolution) as those of solid benzene22 and of nearly the same width. These features indicate that the benzene interacts only weakly with the copper surface, as would be expected for physisorbed molecules. 

Figure 4 shows the effect of benzene-surface interactions parameter, k, on K2 at p = 0.2 for the slitwidth H = 2.0 nm. Negative value of k2s means that the solute molecule has larger adsorption energy. In Fig. 4, the curve of K2 increases with decreasing k as expected. 

Fig. 2.6 Comparison of TPD spectra obtained from a (i -acetylene monolayer on various Sn/Pt(100) surfaces adsorbed at 100 K. Several benzene desorption peaks in the top curve arise from multiple kinetic pathways. Adapted with permission from [54]. Copyright 2001 American Chemical Society...

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