Auxochromes effect

Reactive groups have minimal auxochrome effect on color intensity, and color yield per molecular weight decreases with increasing numbers of reactive groups. Increased dye fixation and reduced environmental impact of hydrolyzed dye more than compensate for color reduction of additional reactive groups. 

Ion-pair extraction and IPC were combined to analyze phosphoric acid mono- and diesters originating from the microbial hydrolysis of flame retardants. Even tertiary treatment did not ensure complete removal of the studied compounds detected in municipal wastewater [107], Chlorophenols extracted from water samples as anionic chlorophenolates were studied by IPC because the anionic forms of these analytes provide better UV ultraviolet absorption than uncharged chlorophenol based on their auxochromic effects. IPC conditions yielded adequate retention of the charged analytes and good sensitivity [108]. 

Phosphorus, whilst having an auxochromic effect, does not transmit conjugation effects from one chromophore to another. Thus the UV spectra of spirobiphenylene-phosphoranes were dominated by the biphenyl ring system. Comparisons of the spectra with the precursor dibiphenylene phos-phonium salt and pentaphenylphosphoranes showed the spirophosphoranes to have more bands than the salt. This was attributed to different auxochromic effects of phosphorus through apical and equatorial bonds. <70JCS(C)1425>. 

The auxochromic effect of an S-atom linked directly to a C=C double bond is reflected in the spectrum of ethylthioethene (X = 229 nm) [19]. A... 

Knott s rule concerns the importance of the place of the nitrogen atom replacing a methine carbon in the conjugated chain when the atom is separated from the active auxochromic atoms by an odd number of conjugated atoms, the shift is bathochromic. It is hypsochromic when there is an even number, Tne importance of the shift could establish a measure of M effect of various heterocyclic nuclei (79. 124). Many papers have been published, and examples have been given to verify these rules (79-84). 

Unsaturated groups, known as chromophores, are responsible for — tz, and k — 7t absorption mainly in the near UV and visible regions and are of most value for diagnostic purposes and for quantitative analysis. The mx and e values for some typical chromophores are given in Table 9.2. The positions and intensities of the absorption bands are sensitive to substituents close to the chromophore, to conjugation with other chromophores, and to solvent effects. Saturated groups containing heteroatoms which modify the absorption due to a chromophore are called auxochromes and include -OH, -Cl, -OR and -NRr... 

In general, auxochromic substitution of chromophores causes bathochromic shifts and increases in intensity for 7t —> k transitions, and hypsochromic or blue shifts (to shorter wavelengths) for n K transitions. The shifts are explainable in terms of mesomeric resonance) effects caused by interaction of lone pair electrons associated with such auxochromes as —OH, —Cl, —NH2 with the k system of the chromophore. This leads to... 

Auxochromes (auxiliary chromophores) are groups which have little UV absorption by themselves, but which often have significant effects on the absorption (both and 8) of a chromophore to which they are attached. Generally, auxochromes are atoms with one or more lone pairs e.g. -OH, -OR, -NR2, -halogen. 

Furan exhibits a single band of medium intensity at 208 nm. Alkylation tends to effect a bathochromic shift of this band to ca. 220 nm as in the many natural products, e.g. difurospinulosin (7), that are /3-alkylfurans. The slight bathochromic shift in the spectrum of [8](2,5)furanocyclophane (69T(25)5357), as compared to 2,5-dimethylfuran, has been ascribed to strain. From the limited data available auxochromic substituents produce little effect on the furan spectrum. 

The data of Table 22-3 show the effect on the benzene chromophore of this type of substituent —the substituent often being called an auxochrome.2 This term means that, although the substituent itself is not responsible for the absorption band, it shifts the absorption of the chromophoric group, in this case the benzene ring, toward longer wavelengths. The auxochromic groups usually increase the intensity of the absorption also. 

Effect of Auxochromic Substituents on Electronic Absorption by the Benzene Chromophore... 

The perchlorates of various secondary amines, such as diphenylamine and indole derivatives, are colorless.64 The similarity of colors produced in the presence of hydrochloric acid also attests to the non-auxochromic character of the perchlorate ion in the production of the colored derivative. Consequently, the only role attributable to the perchloric acid in this test is that with nucleic acids it leads to more effective hydrolysis and releases more 2-desoxyribose for reaction with tryptophan. This reaction leads to the production of a substance of the type represented by XV and XVI (R " = H), and the increase in the number of conjugated double bonds results in the product being colored. With ribose, which has a free hydroxyl group at carbon atom 2, a ketone of the type shown in XVII can be formed, and in this case the net result is no increase in the number of double bonds conjugated with the indole nucleus and no comparable increase in color. Hence the test will distinguish between ribose and 2-desoxyribose. 

When auxochromes such as NHR or OH are present in both rings of the naphthoquinone system, the absorption spectrum consists of two overlapping bands, and this can result in dull colors, typically blue-grays. A 3-cyano group appears to counteract the dulling effect, and 5 [79469-30-0] has been described as a blue dye for polyester [15],... 

A different class of polycyclic naphthoquinone dyes is based on the n apht h 12,361 i ndolizine -6,11 -dione system 14, which is readily accessible by condensation of 2,3-dichloro-l,4-naphthoquinone with active methylene compounds in the presence of pyridine [22], or by reaction of 2-methoxy-3-pyridino-1,4-naphthoquinone with an active methylene compound [23], In 14, the bridgehead nitrogen atom acts as an effective auxochrome, and hence orange to red colors are observed without further substitution. Derivatives of 14 (R = amide group) are of particular value as vat dyes and pigments. Related isomeric heterocyclic structures have also attracted interest, e.g., 15, a yellow disperse dye for polyester [24],... 

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