Chlorin, electronic absorption

The beautiful colors associated with porphyrin and chlorophyll systems are manifest in their characteristic electronic absorption spectra. The most intense band in the spectra, around 400 nm, is known as the Soret band it is intrinsic to the large macrocyclic conjugated pathway and has molar extinction coefficients usually between 150 000-400 000. This extinction value is lower in chlorins than in porphyrins, and the band is absent in porphyrinogens (6) and ring-opened bile pigments. 

Figure 3 Electronic absorption spectra (Soret band omitted) in chloroform a, porphyrin dication (in presence of 0.5% TFA) b, a chlorin...

POCI3 chlorinations (Eq. (8)) are acid-catalyzed reactions of such reaction products]. The hydrogen bonding of azinones is related to that of iV-oxides, discussed below, and to that of ketones (with water and alcohols) and has been demonstrated by infrared measurements on pjn-idinethione in alcohols and by the electronic absorption spectra of azinones in water. 6-Chloro-l,3-dimethyl-pyrimidine-2,4-dione is rapidly aminated at 20° (with heat evolution) by methyl- or ethyl-amines, etc., in protic media (water or alcohols). 

Figure 10. Electronic absorption spectra of purpurin-18 (solid) and chlorin-p6 (dashed)-like compounds isolated from sample 64-481A-2-2 (20).

Fortunately, the ene-ynes are easily recognizable because of their peculiar electronic absorption spectra. In the past we have produced ene-ynes by dehydrohalogenation reactions of chlorinated paraffins [20-22], hence we have acquired a certain specific experience in the field. Furthermore, the spectra of ene-ynes are well known in literature [23-25] starting from the spectrum of mycomycin and its isomer isomycomycin. In the context of the spectra of Figure 18.7(B-D), particularly interesting is... 

For redox and electron-transfer properties of [Os(bipy)j] + and [Os(phen)3] + see p. 539. Osmium(IIJ). Oxidation of [Os(bipy)3] + with chlorine yields the violet [Os(bipy)3] ion," "" while the red [Os(phen)3] is similarly prepared by oxidation of [Os(phen)3] +.Resolution of [Os(phen3)f + has been achieved by oxidation of Ae corresponding [Os(phen)3] species. Spectroscopic properties. The electronic absorption spectra of [Os(bipy)3] " and of [Os(phen)3] " " have been measured, as have their circular dichroism spectra " "" and also Ae spectra of [Os(4,4 -Me2bipy)3] " The lifetimes of the charge transfer (MLCT) excited states of... 

Monomeric alkoxo complexes of W are also known. The dinuclear alkoxo complexes will be discussed in Section 37.4.4. The blue paramagnetic complex [WCl3(OR)2] (R = Me, Et) were first isolated from the reaction of WCU with the corresponding alcohols. t en ethanol is used, the reaction liberates chlorine which oxidizes the ethanol to acetaldehyde as depicted in equations (3) and (4). Chloroalkoxo complexes of W " can also be prepared directly from WCI5 and alcohols at -70 C. Thus, M[WCl4(OR)2] and M[WCls R)] (M = tetraalkyl-ammonium R = Me, Et, Pr") as well as the seven-coordinate M[WCU(OEt)] have been isolated and characterized. Similarly, [WBr4(OMe)2]" has been prepared from WBrs in methanol. The monomeric chloroalkoxo complexes are paramagnetic and exhibit electronic absorption spectra similar to the oxyhalides. 

The electronic absorption spectra of molecular O2F2 and of the radical O2F have been measured in liquid Ar and in other solvents in the region 190—600 nm/° An analysis of the data concerning the nature of the unstable violet and blue compounds that were first reported in 1962 by Streng and Grosse suggests that the colours are due to oxygen fluoride radicals, such as O2F, and not to chlorine oxide fluorides. Thus, it has now been shown that intensely coloured species are formed by O2 salts in liquid HF these species show the same characteristics as the violet and blue compounds . 

The kinetic study " " was performed on RhCl(PPh3)3 and the chlorine-bridged dimer, Rh2Cl2(PPh3)4, with a variety of aldehydes. The progress of the reaction was monitored by UV-VIS electronic absorption spectroscopy at 25 C, and decarbonylation products RhCl(CO)(PPh3)2 and alkane were analyzed. 

If the aUomerization reaction takes place in a slightly alkaline medium and under inert atmosphere, there is only solvolysis of the isocyclic ring, and the resulting components are denominated esterified chlorin es and rhodin g-j, depending on whether they come from the a- or fc-series, respectively. Chlorophyll a yields Mg-phytol-chlorin while pheophytin a or pheophorbide a yields phytol-chlorin eg or free chlorin eg, respectively. The same series of transformations can be described for chlorophyll b. The structural difference between these compounds and the purpurins 7 is solely in the substituent of C-15, which, in place of an O, is an H, so that their coloration, polarity, and electron absorption properties are very similar. Other techniques, such as mass spectroscopy (MS), must be used for their differentiation [28]. 

FIGURE 7.8 Electronic absorption spectra of chlorophyll fl(—) and Mg-phytol-chlorin eg ( ). 

FIGURE 7.10 Electronic absorption spectra of pheophytin a (—) and phytol-chlorin eg (—). 

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