Phenol ultraviolet spectrum

Many of the properties oj -hydroxypyridines are typical of phenols. It was long assumed that they existed exclusively in the hydroxy form, and early physical measurements seemed to confirm this. For example, the ultraviolet spectrum of a methanolic solution of 3-hydroxypyridine is very similar to that of the 3-methoxy analog, and the value of the dipole moment of 3-hydroxypyridine obtained in dioxane indicates little, if any, zwitterion formation. However, it has now become clear that the hydroxy form is greatly predominant only in solvents of low dielectric constant. Comparison of the pK values of 3-hydroxypyridine with those of the alternative methylated forms indicated that the two tautomeric forms are of comparable stability in aqueous solution (Table II), and this was confirmed using ultraviolet spectroscopy. The ratios calculated from the ultraviolet spectral data are in good agreement with those de-... 

Much data on the structure of flavonoids in crude or semipurified plant extracts have been obtained by HPLC coupled with MS, in order to obtain information on sugar and acyl moieties not revealed by ultraviolet spectrum, without the need to isolate and hydrolyze the compounds. In the last decade, soft ionization MS techniques have been used in this respect, e.g., thermospray (TSP) and atmospheric pressure ionization (API). However, the most used methods for the determination of phenols in crude plant extracts were the coupling of liquid chromatography (LC) and MS with API techniques such as electrospray ionization (ESI) MS and atmospheric pressure chemical ionization (APCI) MS. ESI and APCI are soft ionization techniques that generate mainly protonated molecules for relatively small metabolites such as flavonoids. 

The thermolytic deprotection reaction is extremely clean. The infrared spectrum of the deprotected polymer is identical to that of the phenolic precursor as is the ultraviolet spectrum. The molecular weight of the phenolic copolymer precursor is unchanged by the t-BOC protection reaction/thermolysis cycle based on GPC data. 

Predict the effect on the ultraviolet spectrum of a solution of aniline in water when hydrochloric acid is added. Explain why a solution of sodium phenoxide absorbs at longer wavelengths than a solution of phenol (see Tablebelow). ... 

The chemical interpretation of the yellow color in white wines has always been a little-known field. Phenolic compounds are certainly involved, but concentrations are low and their contribution has never really been established. Many studies have investigated the oxidative browning of wines, independently of enzyme mechanisms. Other molecules are involved besides tannins (Sapis and Ribereau-Gayon, 1968), especially compounds that have a high absorption in the visible—and especially ultraviolet—spectrum (Somers and Ziemelis, 1972). Cafeic and coutaric acids are responsible for browning in white wines (Cheynier, 2001). 

The measurement of optic density, absorbance, is widely used to determine wine color (Volume 2, Section 6.4.5) and total phenolic compounds concentration (Volume 2, Section 6.4.1). In these works, the optic density is noted as OD, OD 420 (yellow), OD 520 (red), OD 620 (blue) or OD 280 (absorption in ultraviolet spectrum) to indicate the optic density at the indicated wavelengths. 

Coelenterazine (A) is oxidized into dehydrocoelenterazine (D) by MnC>2 in a mixed solvent of ethanol and ether (Inoue et al., 1977b). Dehydrocoelenterazine (C26H19O3N3) can be obtained as dark red crystals. It does not have the capability of chemiluminescence. The ultraviolet absorption spectrum (Fig. 5.6) shows its absorption maxima at 425 nm (e 24,400) and 536 nm (g 12,600) in ethanol. An addition of NaOH significantly increases the 536 nm peak at the expense of the 425 nm peak. Dehydrocoelenterazine can take a tautomeric structure of quinone type (not shown), in which the phenolic proton on the 2-substituent is shifted onto the N(7) of the imida-zopyrazinone ring. Dehydrocoelenterazine can be readily reduced to... 

By using time-resolved RR spectroscopy with 400-nm laser excitation, the vibrational spectrum of the parent phenoxyl (produced pulse radiolytically in aqueous solution) was observed by Beck and Bras (32), and Tripathi and Schuler (18b). This classic spectrum is shown in Fig. 3. Tripathi (33) has reviewed the early literature. More recently, Spiro and co-workers (34) recorded ultraviolet (UV) RR spectra using 245-nm excitation of systematically isotopically labeled (13C6, and d, 170 isotopomers) phenolate and phenoxyl, and confirmed the assignments of vibrational modes by Tripathi and Schuler (18b). 

Most phenolic glycosides are water soluble, but the corresponding aglycones are usually less so. Phenolic substances are aromatic and therefore show intense absorption in the UV region of the spectrum (2). Most of the benzoic acid derivatives displayed their maxima at 246-262 nm, with a shoulder at 290 - 315 nm, except gallic and syringic acid, which have absorption maxima at 271 and 275 nm, respectively (4). The cinnamic acids absorb in two regions in the ultraviolet, one... 

Phenolic Hydroxyl Group. An ethanolic solution of 3,4,5-tri-methoxybenzyl alcohol (4-0-methylsyringyl alcohol) and sodium hydroxide was prepared, and ultraviolet spectra of the solution were recorded immediately and 3 days after preparation. These spectra were compared with the spectrum of the model compound in neutral ethanol. The three spectra were identical with the absorption curve possessing a broad maximum in the 270-280 m/x region. Further visual observation of the alkaline solution for 2 weeks revealed no color formation. This suggests that phenoxide ion formation may be a necessary initial step in reactions leading to the development of chromophoric structures from lignin model compounds. 

Here we discuss a new class of polypropylene stabilizers—the polymeric phenolic phosphites. These compounds exhibit unique, broad-spectrum activity which may allow simplification of polypropylene stabilizer systems. The most active species are synergistic with thiodipro-pionate esters, are effective processing stabilizers when used alone or with other compounds, and contribute to photostability. Compounds of this type appear to function as both free radical scavengers and peroxide decomposers, and through a mechanism not yet completely understood, allow significant reductions in the concentration of ultraviolet absorbers required to achieve high levels of photostability. 

Figure 3 (Top) Structures of drug A and the known thermal degradation product, referred to as phenol in this report (bottom) ultraviolet/visible absorption spectrum of 0.064 mM drug A in water (dashed line) compared to the combined spectral outputs of the International Conference on Harmonization ultraviolet and visible lamps (solid line).

Phenolic Ethers. Substitution of the phenolic proton by an alkyl group results in a spectrum which closely resembles that of the neutral species of the parent phenol (4). The pesticides that fall into this group are the phenoxy compounds. Table VI shows the Amax values of some important pesticide ethers. The alkyl phenyl ethers do not exhibit a bathochromic shift with pH change into the alkaline range because there is no free phenolic proton to be lost and no charged anion is formed. This represents an important avenue in ultraviolet analysis, in which small amounts of free phenols may be determined in the presence of an excess of the corresponding phenolic ether. Figure 4 shows the spectrum of 2,4-D and its parent phenol, 2,4-dichlorophenol. In an alkaline medium. 

An investigation of the mechanical properties of the irradiated polyamide films showed that the process of photochemical destruction is decelerated by the introduction of such luminophores as 2-(o-hydroxy-phenol)benzoxazole, salol, 7-hydroxymethylcoumarin, the spectra of which correspond to the spectrum of the polyamide. On the other hand, the luminophore o-hydroxybenzaldazine possessing an absorption spectrum corresponding to the spectrum of the polyamides, does not decelerate the photochemical destruction of polyamides, but is a strong sensitizer. The diethyl ester of 2,5-dihydrox3d erephthalic acid, which does not possess a spectrum corresponding to the spectrum of the polyamide, still exerts a protective action in the case of irradiation by filtered ultraviolet light (2900-3200 A). 

---