UV absorption maxima

Table 12 UV Absorption Maxima of Benzisothiazoles (solvent ethanol or methanol)...

Corunnine (127) (73JCS(CC)915) was isolated as violet needles in the course of studies of Spanish Papaveraceae, i.e., Glaucium flavum Cr. var. vestitum (71TL3093). The UV absorption maxima kmax of Corunnine are very similar in ethanol and hydroxide solutions and were found at... 

The Apomorphine-derived alkaloid PO-3 (129) was isolated as violet needles after crystallization from acetone and ether from Papaver orientale (66MI2), but was not found in the green solutions of autoxidized apomorhine hydrochloride (62M941, 68HCA683) (Scheme 51). No anion was detected by elemental analysis. The pA"a of PO-3 is 3.88 0.02 in 50% ethanol. The IR spectrum displays no carbonyl absorption between 1650 and 1700 cm (69MI2). The UV absorption maxima of PO-3 are in agreement with the formulation of a mesomeric betaine [T-max (EtOH) = 310... 

Methylisoquinolinium 2-carboxylate (230), originally prepared by Quast (70LA64), was recently identified as a defensive betaine from Photuris versicolor fireflies (99JNP378). It is a pseudo-cross-conjugated mesomeric betaine isoconjugate to the odd alternant hydrocarbon 2-isopropenyl-naphthalene anion which is an odd alternant hydrocarbon anion. This compound therefore is a member of class 13, which is very rare. The UV absorption maxima Imax (methanol) were found at 235 (4.35), 320 (shoulder, 3.97), and 326 (3.99) nm. This compound undergoes similar reactions as Homarine 19 (Scheme 75). The NMR data are presented in Table VIII. 

Other kinds of conjugated systems, such as conjugated enones and aromatic rings, also have characteristic UV absorptions that are useful in structure determination. The UV absorption maxima of some representative conjugated molecules are given in Table 14.2. 

What conclusion can you draw about the effect of alkyl substitution on UV absorption maxima Approximately what effect does each added alkyl group have ... 

Equilibrium constants for complex formation (A") have been measured for many donor-acceptor pairs. Donor-acceptor interaction can lead to formation of highly colored charge-transfer complexes and the appearance of new absorption bands in the UV-visible spectrum may be observed. More often spectroscopic evidence for complex formation takes the font) of small chemical shift differences in NMR spectra or shifts in the positions of the UV absorption maxima. In analyzing these systems it is important to take into account that some solvents might also interact with donor or acceptor monomers. 

There have been very few systematic studies of the electronic spectra of tetrazolium salts. Generally, they have strong UV absorption maxima... 

While pure erucamide does not exhibit absorption in the 250-280 nm range all commercial products showed UV absorption maxima at 230, 257, 267 and 278 nm (with variable intensities), indicative of the presence of oxidation products (up to 8 wt%) as impurities with chromophoric groups. Colourless impurities do not have an interference effect. 1JV/VIS was also used to evaluate discoloration of 50wt/wt% mixtures of commercial erucamide and inorganic antiblock agents [59]. Apart from the interference by impurities from solvents chemical methods suffer from lengthy procedures. 

Table 4.1 lists synthetic and spectroscopic data for 47-52. It may be seen that the molecular weights (Mw) and UV absorption maxima of the polymers are broadly similar, except for 50, which has a markedly lower Mw, and a weaker, broader, slightly blueshifted UV absorption. This difference appears to result from the structure in that the (.S )-2-methylbutyl groups in... 

It is possible that the helicity is a result of the chiral substitution itself and that the polymers with achiral substituents have, in fact, all-anti conformations. While this possibility cannot be directly ruled out, comparison of the spectroscopic data for the polymers with chiral substituents and achiral substituents, for example, 47 and 48, respectively, indicates similar main-chain dihedral angles, since the UV absorption maxima are so similar. Both polymers should therefore be latent helical, that is, contain segments of opposite screw sense separated by strong kinks (helix reversal points), with the difference being that in the case of 47 the overall numbers of P and M turns are equal, whereas for 48, one of the screw senses predominates, resulting in net helicity and optical activity. 

UV absorption maxima occur at 236, 274 and 316 nm. The molecular formula of zearalenone is C18H22Os, its molecular weight is 318.4 g/mol and its melting point is 162-163°C (Blackwell et al. 1985 Josephs et al. 2003). The maximum fluorescence in ethanol occurs with irradiation at 314 nm and with emission at 450 nm. Its solubility in water is about 0.002 g/100 ml. In an aqueous solution of inositol, the presence of zearalenone can change the crystal structure of this alcohol, which indicates the possibility of interaction between both substances (our observations). Moreover, zearalenone is slightly soluble in hexane and progressively more so in benzene, acetonitrile, methylene chloride, methanol, ethanol and acetone. However, it is readily soluble in aqueous alkali. 

Figure 3 (a) UV absorption spectra of cisoid/anti-aWemai r g oligosilanes with 4-10 Si atoms, (b) Comparison of UV absorption maxima of constrained and unconstrained oligosilanes.13 Reprinted with permission from Tsuji, H. Terada, M. Toshimitsu, A. Tamao, K. J. Am. Chem. Soc. 2003, 125, 25, 7486-7487. 2003 American Chemical Society. 

Complex 69 was prepared in about 60% yield with about 15% metallation and a small drop in molecular weight (from 73,000 for PMPS to 68,000 for 69), which, allowing for the increase in statistical repeat unit, indicates some degradation. Related model compounds based on the coordination of phenyl rings in phenyltrimethylsilane and 1,2-diphenyltetramethyldisilane were compared with 69. The UV absorption maxima (224 and 337 nm) were almost unchanged from those of the precursor PMPS (223 and 338 nm), which possibly reflects the low metal loading as... 

Short alkoxy side-chain polymers are water sensitive, but polymers with long alkyl chains are stable in water, presumably due to the ability of the long alkyl chains to wrap around the core and protect the sensitive Si-O functionality.188 189 These polymers also showed UV absorption maxima red-shifted about 22 nm relative to their... 

The functionalized substrates showed UV absorption maxima at 330 nm, with absorbance directly proportional to the reactive anchor density. The UV absorbance did not decrease on leaving in toluene solution overnight in the dark,... 

It was found that these showed UV absorption maxima at the same wavelength (ca. 395 nm) as their non-chiral-substituted analog, poly(bis- -butylphenylsilylene), as shown in Figure 37, from which it was concluded that the dihedral angles of these polymers were the same.282 The CD spectra showed Cotton effects, thus indicating that the polymers adopted PSS helical conformations and that they do not take all-anti conformations. 

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