Proton-transfer reactions photochemistry

PROTON-TRANSFER REACTIONS IN BENZOPHENONE/ A,A-DIMETHYLANILINE PHOTOCHEMISTRY... 

Proton-Transfer Reactions in Benzophenone/Af,A-Dimethylaniline Photochemistry (Peters). 27 51... 

Proton-Transfer Reactions in Benzophenone/ A, A -Dimethylaniline Photochemistry... 

Case Study 5.1 Mechanistic photochemistry - adiabatic proton transfer reactions of 2-naphthol and 4-hydroxyacetophenone... 

Only in rare instances does an excited molecule reach an Si or Ti spectroscopic minimum of another species by travel on the excited electronic surface, and the return to Sq then produces the new species as a photoproduct. Such "adiabatic photochemistry" is fairly common in proton transfer reactions but is encountered only infrequently among organic photoreactions that involve more substantial structural reorganization. 

Another route to productive CT photochemistry can involve proton transfer reactions between A and D +, which are favored in the redox pair arising from the enhanced acidity of D + (relative to D) and basicity of A (relative to A). Numerous examples of these reactions exist in the organic literature [240-241], and such a pathway should be particularly important for transition-metal hydrides with significantly enhanced acidities of their (metastable) cation radicals [242]. Thus irradiation of the EDA complex of fumaronitrile (as acceptor) with the hydridic donor (CP2M0H2) [35] leads to CT hydro-metallation. 

Yong, H. Photochemistry and proton transfer reaction chemistry of selected cinnamic acid derivatives in hydrogen bonded environments. Int. J. Mass Spectrom. Ion Proc. 1998, 175, 187-204. 

Supramolecular photochemistry, like catalysis, may involve three steps binding of substrate and receptor, mediating a photochemical process (such as energy, electron or proton transfer), followed by either restoration of the initial state for a new cycle or by a chemical reaction (Figure 16). 

In a review of the theories of excited-state proton-transfer (ESPT) reactions, Ar-naut and Formosinho [1] observed that excited-state prototropism as a subject of research has been much less popular, even in the realm of photochemistry, despite its unquestionable importance in fundamental and applied photochemistry. The pace of research in this area has more or less remained the same during all the years since then. 

The 17r<7 states also dominate the photoinduced processes in hydrogen-bonded chromophore-solvent clusters. The photoinduced hydrogen transfer reaction is experimentally and computationally well documented in clusters of phenol and indole with ammonia [14,16,32], There is no clear evidence for the existence of an excited-state proton transfer process in these systems [14], The same conclusion applies to bi functional chromophores solvated in finite clusters, such as 7HQ-ammonia and 7HQ-water clusters [15]. In future work, the photochemistry of larger and biologically relevant chromophores (such as tyrosine, tryptophan, or the DNA bases) should be investigated in a finite solvent environment. 

Unlike the photochemistry of ketones with amine donors, simple thio-ethers often do not lead to the reduction of ketones [183] due to the slower rate of proton transfer from the thioether cation radicals to the ketyl radical anions than back electron transfer. PET reactions of several other sulphur compounds with ketones have been summerised in Mariano s review [11],... 

H -tetramethylbenzidine in anionic-cationic mixed micelles has been studied in detail by ESR . The photochemistry of the semi-oxidised forms of eosin Y and rose bengal have been investigated in colloidal solutions. Relevant to the fluorescence of proteins is a study of fluorescence quenching of indolic compounds by amino-acids in SOS, CTAB, and CTAC micelles O Rate constants for proton transfer of several hydroxyaromatic compounds have been measured in a variety of surfactant solutions. Photoprotolytic dissociation does not require exit of the reactant molecules from the micelles. Micellar solutions can be used to improve the fluorescence determination of 2-naphthol by inhibiting proton transfer or proton inducing reactions z2. jpe decay of the radical pair composed of diphenylphosphonyl and 2,4,6-trimethyl benzoyl radicals in SDS is affected by magnetic... 

Before we proceed to discuss the properties of some of the most common reaction intermediates, we take a look at the simplest of elementary processes encountered in photochemistry electron and proton transfer. 

Fullerenes have very rich photochemistry. Here, several commonly observed photochemical reactions of fullerenes including photoadditions through an electron transfer-proton transfer mechanism and excited state [2-I-2] cycloadditions... 

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