Benzene ultraviolet spectrum

Weber, Th., von Bargen, A., Riedle, E., and Neusser, H. J. (1990), Rotationally Resolved Ultraviolet Spectrum of the benzen-Ar Complex by Mass-Selected Resonance-Enhanced Two-Photon Ionization, J. Chem. Phys. 92,90. 

FIG. 8.4 Determination of the microenvironment of a molecule (a) a portion of the ultraviolet spectrum of benzene in (1) heptane, (2) water, and (3) 0.4 M sodium dodecyl sulfate and (b) ratio of the intensity of the solvent-induced peak to that of the major peak for benzene versus the index of solvent polarity. The relative dielectric constant is also shown versus the index of polarity. (Redrawn, with permission, from P. Mukerjee, J. R. Cardinal, and N. R. Desai, In Micellization, Solubilization and Microemulsions, Vols. 1 and 2 (K. L. Mittal, Ed.), Plenum, New York, 1976.)... 

Figure 8.4a shows a portion of the ultraviolet spectrum of benzene in three media (1) heptane, (2) water, and (3) 0.4 M aqueous sodium dodecyl sulfate. It is not the prominent peaks in these spectra that interest us, but rather the small bands located 3.6 nm on the long-wavelength side of the major features. This band is absent in benzene vapor, but is present with variable intensity in solutions. Accordingly, it is described as a solvent-induced band with an intensity that depends on the polarity of the solvent. 

There is considerable interest in establishing the location within a micelle of the solubilized component. As we have seen, the environment changes from polar water to nonpolar hydrocarbon as we move radially toward the center of a micelle. While the detailed structure of the various zones is disputed, there is no doubt that this gradient of polarity exists. Accordingly, any experimental property that is sensitive to the molecular environment can be used to monitor the whereabouts of the solubilizate in the micelle. Spectroscopic measurements are ideally suited for determining the microenvironment of solubilizate molecules. This is the same principle used in Section 8.3, in which the ultraviolet spectrum of solubilized benzene was used to explore the solvation of micelles. Here we take the hydration for granted and use similar methods to locate the solubilizate. 

A dlatortion of the B2q state of benzene to D j has also been proposed (66) to account for inconsistencies in the interpretation of the ultraviolet spectrum of pure crystalline benzene at low temperatures. Such distortions may be the result of the solid medium or, more probably, the spectral inconsistencies may be due to state splitting by the environment. 

Columns C and D are smaller than A since the volume to be distilled is much less at these stages. The only raw material cost to dry ethanol by this method is for the benzene makeup (to replace process losses), which amounts to about 0.2% of the volume of ethanol produced. Some of this is lost in the dried ethanol, as evidenced by the strong benzene absorption seen in the ultraviolet spectra of absolute alcohol. Thus, for an ultraviolet spectrum free of benzene absorption it is better to use 95% ethanol as the solvent, to avoid this interference. 

Interaction between the electron pair on phosphorus and the benzene ring in triphenylphosphine is indicated by its ultraviolet spectrum (94, 95). 

Tris(3-bromoacetylacetonato)chromium(III) is a dark red-brown crystalline material, which dissolves in benzene to form a green solution. The infrared spectrum of this chelate exhibits a characteristic strong singlet at 1540 cm. i, whereas chromium(III) acetylacetonate exhibits two peaks in this region, at 1560 and 1520 cm. b The ultraviolet spectrum of the brominated chromium chelate in chloroform exhibits a Xmax at 358 m/i(e = 13,070). The brominated chelate is reported to form a stable clathrate complex with chloroform (m.p. 240 to 241°). ... 

Figure 7.12 Ultraviolet spectrum of the S, state of benzene with partially resolved rotational structure. Although the K levels are not resolved, the transition probability is peaked for K = /. The absorption of one additional photon produced the benzene ion. Taken with permission from Kiermeier et al. (1988).

Fig. 17 Ultraviolet spectrum of benzene, showing the secondary band (256 nm) and the two primary bands ( Bj, 183 L, 203 nm).

The absorptions that result from transitions within the benzene chromophore can be quite complex. The ultraviolet spectrum contains three absorption bands, which sometimes contain a great deal of fine structure. The electronic transitions are basically of the n — - n type, but their details are not as simple as in the cases of the classes of chromophores described in earlier sections of this chapter. 

Figure 7.17a shows the molecular orbitals of benzene. If you were to attempt a simple explanation for the electronic transitions in benzene, you would conclude that there are four possible transitions but each transition has the same energy. You would predict that the ultraviolet spectrum of benzene consists of one absorption peak. However, owing to electron-electron repulsions and symmetry considerations, the actual energy states from which electronic transitions occur are somewhat modified. Figure 7.17b shows the energy-state levels of benzene. Three electronic transitions take... 

FIGURE 7.18 Ultraviolet spectrum of benzene. (From Petruska, J., J. Chem. Phys., 34 [1961] 1121. Reprinted by permission.)... 

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