Secondary band

Ultraviolet. Benzene has a series of relatively low intensity absorption bands in the region of 230 to 270 nm. When there is a substituent on the ring with nonbonding electrons, such as an amino group, there is a pronounced increase in the intensity of these bands and a shift to longer wavelength. Aniline shows an absorption band at 230 nm (e = 8600) and a secondary band at 280 nm (e = 1430). Protonation of the amino groups reduces these effects and the spectmm resembles that of the unsubstituted benzene. 

All varieties of color are mainly connected with two main absorption bands in the violet and yellow parts of the spectrum. The secondary bands are also present - in blue and green diapasons. The main absorption bands are connected with F and M-centers. The first one is anion vacancy, which traps electrons and the second is two neighboring anion vacancies with two trapped electrons. The short-wave band in fluorite is generated by mutual absorption of F and M-centers, while the long-wave band is connected with M-center absorption only. In the green varieties the REE (Sm ", Yb and Dy ) are also appreciable. Besides that, the centers O2, O3 and (Y, TR)02 sometimes have influence with resulting yellow and pink colors (Platonov 1979 Krasilschikova et al. 1986). 

X-Ray Diffraction. Powder samples of a single nodule and of several nodules combined gave patterns very similar to those of anthracite (Figure 5). The anthraxolite pattern is broader in the principal peak region, with a pronounced secondary band near 22.5° 2o which is absent from the anthracite pattern. This suggests a wider variation in particle or crystallite sizes present in the anthraxolite. 

Fig. 5.1.3. The relationship between wave numbers and difference molar extinction of secondary bands in the alkaline ionization spectra of lignin-related model compounds. (Lin et al. 1974) Solvent methyl cellosolve-water (80 20, v/v)...

Compound Solvent Primary band Secondary band ... 

Figure 1. (a) Main and (b) secondary bands of the B, vg = 8 (— X, vx =0 excitation spectra. Solid lines experiment, dotted lines simulations. The assignment of the peaks to different nx — ng vibronic transitions are also presented. 

With the high resolution ULPAGIF procedure described by Budowle (30 31)> the primary Gc bands and the secondary Gc bands (Gc-actln complex) easily can be resolved (see ref. 33 for diagram). Careful study of the patterns will permit successful subtyping of Gc derived from bloodstains even with the existence of these secondary bands. 

Unlike Tf derived from serum, Tf from bloodstains present a secondary band for each allelic product. Transferrin has two iron binding sites and the monoferric form of Tf is the most stable. It appears that in bloodstains either binding site is available for iron. Depending upon the site occupied by iron the monoferric forms will have slightly different isoelectric points, and both monoferric forms will exist within a bloodstain. Thus, the monoferric form of Tf will produce two protein bands for each allelic product observed after ULPAGIF. This hypothesis is supported by the fact that these secondary bands do... 

Other symmetry perturbations of the 7t-electron cloud increasing the allowedness of the bands (higher absorptivities) result from substitution in the benzene ring. The bands akin to unsubstituted benzene at 185,210 and 260 nm are usually referred to as the (two) primary bands (or B and LJ and the secondary band (or L ) respectively (Murrell, 1963). Steric repulsions among the substituents and fusion of the benzene system with small rings cause static molecular distortions, and so enhance absorptivity. In some cases this hyperchromic effect is significant, even dramatic. For... 

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

The secondary band is by far the best known. Practically all substituents cause minor bathochromic shifts of this band (7 nm per chlorine). However, in general, the absorptivities are much more sensitive to substituent influences than wavelengths. 

The electronic and vibrational contributions to secondary band absorptivity are nearly separable (Sklar, 1942). Also, the electronic contributions of the substituents are vector-additive. In fact, for every substituent a migra-tional moment (Sklar, 1942), spectroscopic moment (Platt, 1951) or, more... 

In general, the introduction of chlorine in aromatic systems causes small bathochromic shifts in the electronic spectrum (Ballester et al., 1977a, 1980c). Because of them, the secondary band in highly chlorinated benzenes is usually centred around 300 nm (260 nm in unsubstituted benzene). However, because of the bulkiness of chlorine, steric inhibition of resonance is... 

Fig. 22 Benzene-ring perchlorination causes the conjugation (K) band (s 260 nm) of styrene C Hj—CCl=CCl2 to disappear (steric inhibition of styrene resonance). CgCl —CCl=CCl2 displays a benzenoid secondary band (a 305 nm). 

Polychlorinated benzenes show overlapping primary bands and secondary bands around 220-250 and 300 nm respectively. It is well known that in conjugated biphenyls, styrenes and stilbenes, a medium-intense to intense band appears (the so-called K or conjugation band), located between the primary bands and the secondary band. In biphenyls, it is an intense band at 250-270 nm (Fig. 21) in styrenes, in the range 260-280 nm (Fig. 22) and in stilbenes, between 270 and 300 nm (Fig. 23). 

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