RAIRS benzene

We then designed model studies by adsorbing cinchonidine from CCU solution onto a polycrystalline platinum disk, and then rinsing the platinum surface with a solvent. The fate of the adsorbed cinchonidine was monitored by reflection-absorption infrared spectroscopy (RAIRS) that probes the adsorbed cinchonidine on the surface. By trying 54 different solvents, we are able to identify two broad trends (Figure 17) [66]. For the first trend, the cinchonidine initially adsorbed at the CCR-Pt interface is not easily removed by the second solvent such as cyclohexane, n-pentane, n-hexane, carbon tetrachloride, carbon disulfide, toluene, benzene, ethyl ether, chlorobenzene, and formamide. For the second trend, the initially established adsorption-desorption equilibrium at the CCR-Pt interface is obviously perturbed by flushing the system with another solvent such as dichloromethane, ethyl acetate, methanol, ethanol, and acetic acid. These trends can already explain the above-mentioned observations made by catalysis researchers, in the sense that the perturbation of initially established adsorption-desorption equilibrium is related to the nature of the solvent. 

The VEEL spectra of the species formed from cyclohexane on Pt(lll) show that at least two intermediate species occur along the decomposition pathway to benzene. These spectra are discussed in Sections VI.A and VI.C, in the context of spectra of species formed from adsorbed cyclohexene (239) and cyclo-l,3-hexadiene (240) on the same surface. On Pt(100) hex, in contrast to Pt(lll), most of the cyclohexane molecules desorb before conversion to benzene, but the latter was formed after adsorption at 300 K. An intermediate in the conversion of cyclohexane into benzene on Pt(100) (1 X 1), stable between ca. 200 and 300 K, was recognized spectroscopically, but not structurally identified, by RAIRS (230) and by VEELS (224). It seems that there is a smooth transition from the spectrum of adsorbed cyclohexane on Pd(100) to that of benzene at temperatures exceeding 250 K without the detection of intermediate spectra (220). 

More recently, two papers have described higher resolution RAIRS results for benzene on Pt(lll) (311, 312) and on Cu(110) (312). The latter spectra, obtained by Haq and King, were particularly informative in relation to VEELS results characterizing the same system obtained earlier by Leh-wald et al. (284). Furthermore, Raman spectra have been obtained for C6D6 on Ag(lll) and Ag(110) (313). 

Figure 14. IR absorption spectra of the protected HS-PPB-SH (AcS-PPB-SAc) in the bulk solid phase (A, left axis) compared to die RAIRS spectrum of HS-PPB-SH self-assembled on gold slides (B, right axis). (I) shows the 6(X)-2300 cm region, (2) shows the 2800-3200 cm region. The bands associated to the protecting group (v[C=0], v[CH,]) disappear in the oligomer SAM, due to the in-situ deprotection via base-promoted hydrolysis. The v[C—H] associated with the benzene rings (see Table 3) is absent or occasionally very weak in the SAM spectrum. Scan parameters (A) 30 scans, 1cm resolution (B) 1000 scans at 84° incidence, 4 cm resolution. The spectra were collected in a spectrometer purged with N, to minimize the signal from water vapor and then baseline corrected.

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