Protonation photochemical

A light-driven compound containing a photosensitizing tetraphenylporphyrin group linked to a diiron azadithiolate moiety (25) has been synthesized as a model compound of iron-only hydrogenases. This compound reduces protons photochemically to hydrogen.392... 

The regioselectivity of addition of HBr to alkenes under normal (electrophilic addi tion) conditions is controlled by the tendency of a proton to add to the double bond so as to produce the more stable carbocatwn Under free radical conditions the regioselec tivity IS governed by addition of a bromine atom to give the more stable alkyl radical Free radical addition of hydrogen bromide to the double bond can also be initiated photochemically either with or without added peroxides... 

Azirine, trans-2-methyl-3-phenyl-racemization, 7, 33, 34 1-Azirine, 2-phenyl-reactions, 7, 69 with carbon disulfide, S, 153 1-Azirine, 3-vinyl-rearrangements, 7, 67 Azirines, 7, 47-93 cycloaddition reactions, 7, 26 fused ring derivatives, 7, 47-93 imidazole synthesis from, 5, 487-488 photochemical addition reactions to carbonyl compounds, 7, 56 photolysis, 5, 780, 7, 28 protonated... 

Paal-Knorr synthesis, 4, 118, 329 Pariser-Parr-Pople approach, 4, 157 PE spectroscopy, 4, 24, 188-189 photoaddition reactions with aliphatic aldehydes and ketones, 4, 232 photochemical reactions, 4, 67, 201-205 with aliphatic carbonyl compounds, 4, 268 with dimethyl acetylenedicarboxylate, 4, 268 Piloty synthesis, 4, 345 Piloty-Robinson synthesis, 4, 110-111 polymers, 273-274, 295, 301, 302 applications, 4, 376 polymethylation, 4, 224 N-protected, 4, 238 palladation, 4, 83 protonation, 4, 46, 47, 206 pyridazine synthesis from, 3, 52 pyridine complexes NMR, 4, 165... 

The dienol is unstable, and two separate processes have been identified for ketonization. These are a 1,5-sigmatropic shift of hydrogen leading back to the enone and a base-catalyzed proton transfer which leads to the / ,y-enone. The deconjugated enone is formed because of the kinetic preference for reprotonation of the dienolate at the a carbon. Photochemical deconjugation is a synthetically useful way of effecting isomerization of a,) -unsaturated ketones and esters to the j ,y-isomers. 

The Hofmann-Loffler-Freytag reaction represents formation of pyrrolidines or piperidines by thermal or photochemical decomposition of protonated A -haloamines in the presence of strong acid such as sulfuric acid or trifluoroacetic acid. " The Hofmann-Loffler-Freytag reaction may also be carried out in milder conditions, for example, PhI(OAc)2,12, hv as shown in section 2.3.4. 

An intramolecular photochemical proton-transfer mechanism has also been postulated by W. C. Clark and G. F. Lothian [7Vans. Faraday Soc. 54, 1790 (1958)]. 

Prostaglandins 624, 725, 960 Prostanoids 620 Protonation 565-567, 1049 photochemical 882 Pseudopotential methods 15, 16 Pummerer rearrangement 240, 243, 470, 843 Pyramidal inversion 602, 604 Pyrazolenines 749 Pyridazine oxides 640 Pyridine aldehydes, synthesis of 310 Pyridine oxides 640 Pyrolysis 102-105 of sulphones 110, 679-682, 962 of sulphoxides 739, 740 Pyrroles 265, 744... 

Photochemical alkylation of protonated quinoline occurred with Ph2Se(02Cc-... 

The sequential electron-proton-electron transfer mechanism is in agreement with the experimental observation by Ohno et al. [141]. The mechanism was confirmed by Selvaraju and Ramamurthy [142] from photophysical and photochemical study of a NADH model compound, 1,8-acridinedione dyes in micelles. 

The photochemically active bands of methylcobalamin have been identified as the intense hands due to -n—n transitions within the conjugated corrin ring, and the following quantum yields (< ) were obtained A = 490 nm, Similar quantum yields ( = 0.3-0.5) were also obtained for the photolysis of methylcobalamin in acid, where the base has been displaced and protonated, and the complex is present as a mixture of the methylaquo and five coordinate methyl complexes (/40). The effect of varying the second axial ligand on the rate of photolysis by white light has also been studied (134). 

Bronsted acidity is the principal source of activity with the relative concentration of protonated and non-protonated reactants being dependent upon the nature of the exchangeable cation. Using FeCls - graphite intercalates - formed using a photochemical procedure and subsequently reduced using K/naphthalide - an efficient catalyst for the production of acetylene from syngas has been produced. 

Carbenes from Sulfonylhydrazones. The second method listed in Scheme 10.8, thermal or photochemical decomposition of salts of arenesulfonylhy-drazones, is actually a variation of the diazoalkane method, since diazo compounds are intermediates. The conditions of the decomposition are usually such that the diazo compound reacts immediately on formation.147 The nature of the solvent plays an important role in the outcome of sulfonylhydrazone decompositions. In protic solvents, the diazoalkane can be diverted to a carbocation by protonation.148 Aprotic solvents favor decomposition via the carbene pathway. 

Formosinho, S. J. Amaut, L. G. Excited-state proton transfer reactions. II. Intramolecular reactions. J. Photochem. Photobiol. A Chem. 1993, 75, 21—48. 

Brousmiche, D. W. Wan, P. Excited state (formal) intramolecular proton transfer (ESIPT) in p-hydroxyphenyl ketones mediated hy water. J. Photochem. Photobiol. A Chem. 2000, 130, 113-118. 

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