Color rational

Compound Prepa- ration" Temperature (°C) Time (days) Color (g/cm ) Ref. 

Indigo is the most important vat dye, dating back to ancient times and produced on an industrial scale since 1880. To replace the indigo dyes, the indanthrone (21) class of dyes was developed. Indanthrone has superior characteristics as a vat dye and became a key material for further development of anthraquinoid vat dyes. There exist a variety of anthraquinone vat dyes differing in the chromophoric system. The color-structure relationship of vat dyes have been rationalized by the Pariser-Parr-Pople molecular orbital (PPP MO) method. Some examples of commercialized anthraquinoid vat dyes are shown in Scheme 6.14... 

Since 1975, porphyrin complexes of all metals of the periodic table of elements are known, with the exception of some actinoids (20-22). The most fascinating property of all metalloporphyrins is their intense color porphyrlike in the solid state, brick-red, pinkish red, olive-green, or brown in dilute solutions. The absorption spectra vary with the metal, the porphyrin, and the axial ligand many attempts to rationalize the different types of spectra have been undertaken (20-22, 24, 42-48). As the. .periodic table of metalloporphyrins (24) is now nearly complete, a new approach... 

The addition reactions of thiolates to NP are generally followed by the decomposition of the red adducts. A survey on the persistence of the red colors showed that the adduct with thiosuccinic acid was extremely stable over days (118). Some rationalization on the different adduct stabilities has been advanced thus, the presence of electron-rich or electron-withdrawing groups on the thiolate anion destabilize or stabilize the adducts, respectively. The great stability of the thiosuccinic acid adduct with NP has shown to be valuable for the quantitative determination of the nitrosyl complex (34,35). 

When petroleum occurs in a reservoir that allows the crude material to be recovered by pumping operations as a free-flowing dark to light colored liquid, it is often referred to as conventional petroleum. Heavy oils are the other types of petroleum that are different from conventional petroleum insofar as they are much more difficult to recover from the subsurface reservoir. The definition of heavy oils is usually based on the API gravity or viscosity, and the definition is quite arbitrary although there have been attempts to rationalize the definition based upon viscosity, API gravity, and density. 

The third radical cation structure type for hexadiene systems is formed by radical cation addition without fragmentation. Two hexadiene derivatives were mentioned earlier in this review, allylcyclopropene (Sect. 4.4) [245] and dicyclopropenyl (Sect. 5.3) [369], The products formed upon electron transfer from either substrate can be rationalized via an intramolecular cycloaddition reaction which is arrested after the first step (e.g. -> 133). Recent ESR observations on the parent hexadiene system indicated the formation of a cyclohexane-1,4-diyl radical cation (141). The spectrum shows six nuclei with identical couplings of 11.9G, assigned to four axial p- and two a-protons (Fig. 29) [397-399]. The free electron spin is shared between two carbons, which may explain the blue color of the sample ( charge resonance). At temperatures above 90 K, cyclohexane-1,4-diyl radical cation is converted to that of cyclohexene thus, the ESR results do not support a radical cation Cope rearrangement. 

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