Phenol electronic absorption spectrum

Since the suggestion of the sequential QM/MM hybrid method, Canuto, Coutinho and co-authors have applied this method with success in the study of several systems and properties shift of the electronic absorption spectrum of benzene [42], pyrimidine [51] and (3-carotene [47] in several solvents shift of the ortho-betaine in water [52] shift of the electronic absorption and emission spectrum of formaldehyde in water [53] and acetone in water [54] hydrogen interaction energy of pyridine [46] and guanine-cytosine in water [55] differential solvation of phenol and phenoxy radical in different solvents [56,57] hydrated electron [58] dipole polarizability of F in water [59] tautomeric equilibrium of 2-mercaptopyridine in water [60] NMR chemical shifts in liquid water [61] electron affinity and ionization potential of liquid water [62] and liquid ammonia [35] dipole polarizability of atomic liquids [63] etc. 

Nanosecond Flash Photolysis Measurements.—A computer-controlled ns flash photolysis spectrometer has been described. " The system was employed in a study of the photochemistry of xanthene dyes in solution. A nitrogen laser was used to provide 2—3 mJ excitation pulses at 337.1 nm for a ns flash photolysis study of electron-transfer reactions of phenolate ions with aromatic carbonyl triplets. " A PDP II computer was used to control the transient digitizer employed for detection, and to subsequently process the data. A nanosecond transient absorption spectrophotometer has been constructed using a tunable dye laser in a pulse-probe conflguration with up to 100 ns probe delayA method for reconstructing the time-resolved transient absorption was discussed and results presented for anthracene in acetonitrile solution. The time-resolution of ns flash photolysis may be greatly increased by consideration of the integral under the transient absorption spectrum. Decay times comparable to or shorter than the excitation flash may be determined by this method. 

Identification of the Transients. Neutral Solutions. In deaerated 5 X 10"5M p-nitrophenol solution at pH 7, the absorption spectrum with a maximum at 290 n.m. was observed about 20 /xsec. after the end of the radiation pulse (Figure 1-A) when all the hydrated electrons, H and OH radicals have reacted with the p-nitrophenol. The spectra shown in Figure 1-A and 1-B were corrected for the decrease in optical density owing to solute destruction. The G-value for the destruction of p-nitro-phenol was assumed to be equal to the sum of G(e"aq) + G(OH) + G(H) = 6.0 (2, 15, 19). The corrections had a maximum value at 400 n.m. namely, 103% and 130% of the observed optical densities and decreased to 40% and 81% at 290 n.m. for spectrum A and B, respectively. When hydrated electrons are converted to OH radicals by reaction with N20 (II), the absorption at 290 n.m. decreases and the maximum shifts towards 300 n.m. (Figure 1-B). It can be concluded, therefore, that the transient species produced by hydrated electrons as well as OH radicals have an optical absorption in the same wavelength region. 

The 2,6-xylenol content is determined using the second derivative - difference absorption spectrum of its phenolate as the peak amplitude, D2, at wavelengths of 302.0 -312.5 nm. The calibration constant, K.2 = D2/C2, was found to be 5.71 x 10 mg dm (SD = 0.07 X 10" mg dm ) calculated from six measurements). The positions of the maxima on the second derivative curves are influenced by the mode of derivation (electronic, microcomputer) and by the setting of the spectrophotometer controls. 

The formation of coordinated phenoxyls in the monocations and dications, [Fe(L )]+ and [Fe(L )]2+, is clearly demonstrated by their electronic spectra (142). Fig. 23 displays the spectra of [Fem(LBuMet)]°, [Fe(LBuMet )]+, and [Fem(LBuMet )]2+. Since the spectrum of the neutral tris(phenolato)iron(III) species shows an absorption minimum at -400 nm it is significant that the monocation and dication both display a new intense asymmetric maximum in this region. This intense maximum is the fingerprint of phenoxyl radicals. It is also remarkable that this maximum doubles in intensity on going from the monocation to the dication. On increasing the oxidation level stepwise, the phenolate-to-iron CT band experiences a batho-chromic shift from 513 nm in the neutral species to 562 nm in the monocation and... 

A predominant toxin (51) from water beetles of the genus llybius (Table V) shows a UV absorption corresponding to hydroxyquinoline or hydroxyiso-quinoline. The H-NMR spectrum exhibits, beside signals of methyl ester and phenol, signals of five aromatic protons as both ABC and AB systems, the latter indicating two protons at C-3 and C-4 in quinoline. Since electron pyrolysis of 51 gives radioactive 8-hydroxyquinoline, its structure is identified as methyl 8-hydroxyquinoline-2-carboxylate (51) and confirmed by synthesis from xanthurenic acid (52) (Scheme 48) (101). The precursor of this alkaloid was shown to be tryptophan (444). 

The d-d absorption of the copper complex differs in each step of the catalysis because of the change in the coordination structure of the copper complex and in the oxidation state of copper. The change in the visible spectrum when phenol was added to the solution of the copper catalyst was observed by means of rapid-scanning spectroscopy [68], The absorbance at the d-d transition changes from that change the rate constants for each elementary step have been determined [69], From the comparison of the rate constants, the electron transfer process has been determined to be the rate-determining step in the catalytic cycle. 

The practical limitations in the Z-value approach can be overcome by using pyridinium A -phenolate betaine dyes such as (44) as the standard probe molecule. They exhibit a negatively solvatochromic n n absorption band with intramolecular charge-transfer character cf. discussion of this dye in Section 6.2.1, its UV/Vis spectrum in Fig. 6-2, and its dipole moment in the electronic ground and excited states mentioned in Table 6-1, dye no. 12. 

Substitution of benzene with polar groups containing unshared electrons (auxochromes like OH or NH2). shifts the absorption bands to longer wavelengths and also intensifies them. The spectra of phenol and aniline in heptane solution are reproduced ifl Figwes 5.1 and 5.2. The vibrational structure of the 260 m/x band is not seen in the aniline spectrum. In general, the fine structure of the 260 m/x band disappears in polar solvents when the... 

Demethylsonodione (7), a p-quinonoid aporphine, was obtained as greenish prisms. Its molecular formula was determined as C19H17O5N by high-resolution electron impact mass spectrometry (HREIMS) at m/z 339.1098 [M]+ [24]. The UV spectrum with maxima at 219, 283, 336, and 642 nm was typical of a p-quinonoid aporphine skeleton [53]. In its IR spectrum, absorption bands at 3440 cm 1 (phenolic hydroxyl) and 1635 cm 1 (carbonyl) were apparent. The H-NMR spectrum indicated signals... 

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