Benzene bands

The basis for the further assignment of the bands to specific vibrations is the assignment of the benzene bands given by Whiffen (1955) on the basis of an exact molecular model calculation. 

Fig. 2 displays a set of FTIR spectra obtained for the uptake of benzene into H-ZSM-5 at 415 K employing the experimental device and procedure as described in the Experimental Section. One recognizes the increase in absorbance of the typical benzene band at 1478 cm as a function of time (spectra 1 to 4). The maximum absorbance, A, of such bands can be used as a measure of the amount sorbed, M, at time t into the porous structure of the zeolite crystallites. Therefore, evaluation of the sequence of these spectral uptake curves can provide data which may be used in the appropriate solution (equ. 1) of Fick s second law, and this generates the desired diffusivities [22] ... 

Tables II-VII give frequencies in wave numbers of benzene bands which lie near emission lines of mercury. Included are assignments in lower and upper states to vibrational levels as given by Ingold and his co-workers. Most experimental work is based on mercury lamps of one type or another. In using them to obtain monochromatic light either color filters...

Benzene itself of course exhibits absorption in the near ultraviolet. Substituted benzenes, such as nitrobenzene, have more extensive absorption bands in about the same region of the spectrum. Now if we compare the absorption curves of three isomeric di-substituted benzenes, we should see whether deviations occurring in the orfAo-position manifest themselves in the benzene bands or e.g. for nitrobenzene in the nitro-band or in both. 

If we then consider the nitrophenols and nitro-anisoles we find that they behave in an entirely different way. To begin with, the absorption band of anisole is shown in fig. 2. Here the rise of the first benzene band is as steep as in benzene itself and as in the chloro-... 

Fig. 3 Comparison of absolute MIES peaking intensities of the 0(2p) + le,j [0(2p)+B,] structure and the lajySejg (Bj) and lb2 /3e (B3) benzene bands. The plotted between intensities (valleys between the peaks) denote the background intensity.

When the substituent on the benzene nucleus is a chromophore like the carbonyl group, the absorption bands are shifted towards the red just as in the case of vinyl substituion. A weak band due to the n -> tt transition of the chromophore (R-band) is also observed at longer wavelengths (e.g. acetophenone, azobenzene, see Table 52). The bands of carbonyl compounds are completely submerged by the 260 mp benzene band if the spectra are... 

Group % meta in I nitration i Amax, m/t1 (200 m/t benzene band) Spectroscopic moment14... 

Table 9-1 provides retention volume data for several sample compounds in a model GAC system (benzene plus helium carrier gas) and the corresponding GSC system (helium carrier gas data of Fig. 9-1). For every sample compound, the use of the adsorbing carrier gas decreases its retention volume, and this is fairly typical of GAC separation. Increasing the concentration of benzene in the carrier gas further decreases C/ for all the compounds of Table 9-1, implying that partition effects [case (4)] are relatively unimportant. With the exception of the weakly adsorbing alkanes and those samples with retention volumes smaller than that of benzene (the carrier gas component), the GAC system of Table 9-1 gives two elution bands when a single sample compound is injected into the column. One band corresponds to the injected compound and the other is a benzene band. For these latter compounds it is apparent that adsorption proceeds (at least in part) by case (3) adsorption of the sample... 

It is well known that resonance and induction have a marked effect on orientation in aromatic substitution. A correlation between orientation in substitution and electronic absorption spectra of benzene derivatives would be expected. Table 7.6 shows data for the position of the 200-nm benzene band [8, 9] as compared with the percentage of the meta isomer produced in nitration. 

Table 7.6. Variation in Position of the 200-nm Benzene Band with Percentage of the Meta Isomer Produced in Nitration...

Substituent Meta in Nitration (percent) Amai (nm) of 200-nm benzene band... 

Fig. 7. Calibration curve for the extinction coefficient of benzene sorbed into zeolite H-ZSM-5 integrated absorbance of the typical benzene band at 1478 cm" vs. the barometrically measured amoimt adsorbed [132]...

Tris(p-8ubstituted)phenylbenzoylsilanes have an intense absorption in the region of 220-230 m/x (e 40,000), which is possibly the primary benzene band, shifted to longer wavelengths by the p-substituents. 

The second band of this series falls between 1588—1560 cm" Unlike the parallel benzene band it is usually of medium intensity and its appearance is not therefore necessarily related to conjugation. The separation of this pair of bands is about 40 cm" for 4-alkyl pyridines but about 20 cm" for the 2- and 3-compounds [41 ]. 

N-H/C-N/C=0 [2 X amide I (2vC=0 stretching) and amide III deformation (C-N stretching/N-H in-plane bending) combination] for gamma-val olactam CHv-tCCV (15 + 9), benzene band assignment... 

C-H aromatic C-H (aryl) CCv-tCHv (13 + 15), benzene band assignment C-H aryl... 

---