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204690-28-8

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204690-28-8 Usage

Check Digit Verification of cas no

The CAS Registry Mumber 204690-28-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,0,4,6,9 and 0 respectively; the second part has 2 digits, 2 and 8 respectively.
Calculate Digit Verification of CAS Registry Number 204690-28:
(8*2)+(7*0)+(6*4)+(5*6)+(4*9)+(3*0)+(2*2)+(1*8)=118
118 % 10 = 8
So 204690-28-8 is a valid CAS Registry Number.

204690-28-8Relevant articles and documents

Nonlinear solvent water effects in the excited-state (formal) intramolecular proton transfer (ESIPT) in m-hydroxy-1,1-diaryl alkenes: Efficient formation of m-quinone methides

Fischer, Maike,Wan, Peter

, p. 4555 - 4562 (1999)

The photohydration of hydroxy-substituted 1,1-diaryl alkenes 1-3 has been studied in aqueous CH3CN solution. Evidence for formation of quinone methide intermediates was provided by product studies and by observation of its absorption spectrum by laser flash photolysis. For the meta isomers, the proposed mechanism of m-quinone methide formation probably involves a solvent-mediated ("proton-relay") excited-state (formal) intramolecular proton transfer (ESIPT) from the phenol hydroxyl group to the β-carbon of the alkene moiety in neutral aqueous CH3CN solution, either in a concerted manner or via two very fast steps. The m-quinone methides are then trapped by water to form the corresponding diaryl ethanol product with high overall quantum yield. Evidence for the ESIPT pathway was provided by fluorescence and LFP measurements. The addition of small amounts of water (3CN) decreased the fluorescence emissions of 1 and 2 with a concomitant increase in production of m-quinone methides. Stem-Volmer analyses of fluorescence data revealed a dynamic and a minor static quenching component, both of which involved a water trimer cluster. The degree of charge transfer from the phenol (phenolate) oxygen to the alkene β-carbon, which may be thought of as the driving force for this efficient ESIPT, is pronounced for the meta isomer in the excited state, consistent with Zimmerman's "meta-ortho effect". Alkenes 1 and 2 were shown to be more efficient in m-quinone methide photogeneration than the hydroxy-substituted benzyl alcohol 8, which required conditions of higher water content for similar quantum yields.

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