Phenols electronic spectra

In the last few years McCleverty, Ward, and co-workers have reported the NIR electrochromic behavior of a series of mononuclear and dinuclear complexes containing the oxo-Mo(iv) v core unit [Mo(Tp )(0)Cl(OAr)], where Ar denotes a phenyl or naphthyl ring system [Tp = hydro-hydrotris(3,5-dimethylpyrazolyl)borate].184-189 Mononuclear complexes of this type undergo reversible MoIV/Mov and Mov/MoVI redox processes with all three oxidation states accessible at modest potentials. Whilst reduction to the MoIV state results in unremarkable changes in the electronic spectrum, oxidation to MoVI results in the appearance of a low-energy phenolate- (or naphtholate)-to-MoVI LMCT process.184,185... 

Rev. The diamagnetic RevO-OEP-fluoride produces an electronic spectrum [614 (3.76), 582 (3.92), 464 (4.64), 338 (4.81)], possibly indicative of an Mnin-type system. The peak at 338 nm, or at least its high extinction, may not be real, however, because many of the authors complexes have been measured in benzene or prepared in phenol so that aromatic compounds could largely account for this peak [Buckler (27)]. 

Fig. 12 Schematic structure of the model 5-coordinate heme-mimicking nitrosyl complex (a), its orbital diagram showing the predicted electronic transitions (b), and its experimental and calculated electronic spectrum (c). R = -C2H2- or o-phenolate MO labels are derived from a B3LYP/ TZVP calculation. Reprinted from the reference [115], with the permission of Elsevier Science Ltd., copyright 2012...

We have studied demulsifier association by the electron spin resonance (ESR) technique. The spin label is covalently attached (Figure 5a) to the demulsifier. Normally, the ESR spectrum of a freely tumbling nitroxyl radical consists of three sharp peaks (Figure 5b). However, the spectrum for a tagged ethoxylated nonyl phenol resin (Figure 6a or 6b) shows only a single broad peak. 

From the 351-nm photoelectron spectrum of the phenolate anion, the electron affinity of the phenoxyl has been determined to be 2.253(6) eV. The first excited state of the phenoxyl radical appears at 1.06(5) eV above the ground state (51). 

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... 

Plastocyanin from parsley, a copper protein of the chloroplast involved in electron transport during photosynthesis, has been reported to have a fluorescence emission maximum at 315 nm on excitation at 275 nm at pH 7 6 (2°8) gjncc the protein does not contain tryptophan, but does have three tyrosines, and since the maximum wavelength shifts back to 304 nm on lowering the pH to below 2, the fluorescence was attributed to the emission of the phenolate anion in a low-polarity environment. From this, one would have to assume that all three tyrosines are ionized. A closer examination of the reported emission spectrum, however, indicates that two emission bands seem to be present. If a difference emission spectrum is estimated (spectrum at neutral pH minus that at pH 2 in Figure 5 of Ref. 207), a tyrosinate-like emission should be obtained. 

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 chromophore of phenylephrine is not extended but its structure includes a phenolic hydroxyl group. The phenolic group functions as an auxochrome under both acidic and alkaline conditions. Under acidic conditions it has two lone pairs of electrons, which can interact with the benzene ring and under basic conditions it has three. Figure 4.11 shows the bathochromic and hyperchromic shift in the spectrum of phenylephrine, which occurs when 0.1 M NaOH is used as a solvent instead of 0.1 M HCl. Under acidic conditions the X max is at 273 and has an A (1 %, 1 cm) value of 110 and under alkaline conditions the X max is a 292 nm and has an A (1%, 1 cm) value of 182. 

The anomeric phenyl glycosides (5) and (6) afford practically identical mass spectra. A characteristic feature of the mass spectra of the phenyl glycosides is the strong increase of intensity of the series A fragments (m/e 219, 187, 155) and of the E (m/e 111) fragment. These ions are formed by elimination of the phenoxyl grouping as phenol or as the C H60 radical the latter is rather stable, due to interaction of the odd electron with the benzene ring. At the same time, peaks of the series B, C, D, and E (except E ) become less intense, or even disappear completely from the mass spectrum. 

Phenols usually give a strong molecular ion. Typical peaks in the spectrum arise from M — 28 (CO), which is a useful odd-electron ion, and M — 29 (CHO). 

Those solutes for which the solvent shifts are particularly large have been used in the specification of solvent properties, such as electron-pair donation ability, Lewis basicity, or softness. For the former property, the solvent shifts of deuteromethanol or of phenol have served as suitable scales. For the latter property the solvent shifts of the symmetrical stretch of Hg-Br in the Raman spectrum of HgBr2 and of I-CN in the infrared spectrum of ICN have been so employed (see Chapter 4). 

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. 

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