1.4- dimethoxybenzene DMB

Photoinduced oxidation of 1,4-dimethoxybenzene (DMB) and tetrahydrofuran (THF) by [Au(C N N-dpp)Cl]+ in acetonitrile upon UV/Vis irradiation have been observed. The time-resolved absorption spectrum recorded 12 (xs after excitation of [Au(C N N-dpp)Cl] with a laser pulse at 35 5 nm showed the absorption band of the DMB radical cation at 460nm, whereas upon excitation at 406 nm in the presence of THF, a broad emission characteristic of the protonated salt of 2,9-diphenyl-l,10-phenanthroline (Hdpp ) developed at 500 nm. 

Fig. 3. Temperature and concentration dependence of the line broadening observed for the methoxy signal of 1,4-dimethoxybenzene (DMB) during the electron transfer quenching of triplet decafluorobenzophenone by DMB in acetonitrile-d3 [178]...

In fact, the addition of 1,4-dimethoxybenzene (DMB) and/or several similar compounds, at concentrations as low as 10 4 M, to a mixture of aryl-olefins and DCA almost completely inhibits the reactions. Concentration dependence and flash photolysis studies confirm that the primary electron-transfer process occurs between the singlet excited sensitizer and DMB (E01 = 1.34 V vs SCE) with the generation of the corresponding radical ion pair. As a consequence, quantum yields lower than 1, even at infinite substrate concentration, are measured [95]. In this regard, valuable confirmations came from the cyanoaromatic photoinduced electron-transfer oxygenation of alkynes [99], Farid and Mattes reported that the photooxygenation of diphenylacetylene DPA (E° = 1.85 V vs SCE) 25, leading to a mixture of benzil 26 and benzoic acid 27, was efficiently sensitized by DCA ( = 0.15), but poorly by TCA ( > < 0.001) [Eq. (12)] [99]. 

In fact, the addition of 1,4-dimethoxybenzene (DMB) (0.13 equiv.), easier to oxidize than 21, appreciably quenches the reaction. The laser flash photolysis with a nitrogen-pulsed laser (337 nm) of a TPP+BF4 (1.6 x 10-4 M) dichloromethane solution, in the presence of 21 (6.2 x 10 2 M), conditions in which nearly 80% of the singlet excited sensitizer (Ered = 0.29 V vs SCE) is quenched by 21, gives a transient absorption (A 550 nm) assigned to a pyranil radical TPF. 

Figure 62. (a) Two trichromophoric systems used for investigating through-solvent-mediated charge recombination processes, (b) Profiles of the (U)HF/3-21G gas-phase structures of the CS state (left) and ground state (right) of an analogue of synSS in which the dimethylaniline donor is replaced by 1,4-dimethoxybenzene (DMB). 

The diphenylphenanthroline complex 23 is emissive in fluid solutions, with quantum yields of ca. 10-4 and lifetimes of 0.4-0.7 ps. The estimated excited state reduction potential of 2.2 V (vs. normal hydrogen electrode (NHE)) suggested that the complex is a strong photooxidant, which was demonstrated with the formation of the 1,4-dimethoxybenzene radical cation (DMB+) upon UV-visible irradiation of an MeCN solution of the complex with DMB.22... 

Synonyms Anisole, p-methoxy- Benzene, 1,4-dimethoxy- 1,4-Dimethoxybenzene Dimethyl ether hydroquinone Dimethyl hydroquinone Dimethylhydroquinone ether DMB DMHQ HQDME Hydroquinone dimethyl ether p-Methoxyanisole Quinol dimethyl ether Classification Aromatic ether Definition Obtained by methylation of hydroquinone using dimethyl sulfate and alkali Empirical CsHio02 Formula C6H4(OCH3)2... 

A stable adduct of Cjq with an electron donor moiety in the side chain (Table 4.1, compound 7) [24] was synthesized by the cycloaddition of a rigid diene containing a polynorbornyl-bicyclo[2.2.0]hexyl bridge and a dimethoxybenzene (DMB) unit in toluene at reflux in 63% yield. The donor-acceptor interaction of the electron rich DMB unit and Cjq is indicated by the X-ray crystal structure. The adducts are paired... 

The major advantage of DMB is the superior sensitivity for most a-keto acids detection limits of 6-29 fmol per 5 pi sample volume are reported [428]. Similarly, 1,2-diamino-4,5-dimethoxybenzene and l,2-diamino-4,5-ethylenedioxybenzene can be used for the determination of a-keto acids. 

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