Isomerization, of unsaturated

These pentahydrides have attracted attention as catalysts for hydrogenation of the double bond in alkenes. IrH5(PPr3)2 catalyses vinylic H-D exchange between terminal alkenes and benzene, the isomerization of a,f3-ynones, isomerization of unsaturated alcohols and dehydrogenation of molecules such as secondary alcohols [176],... 

A final, rather different example which fits in appropriately here, in that it involves hydrogen exchange, is the measurement of equilibrium and rate constants for the base-catalyzed isomerization of unsaturated sulfides, sulfoxides and sulfones193 ... 

In this article, the features and mechanism of the crystal-to-crystal reactions of 1,3-diene compounds are described on the basis of the molecular packing structure and intermolecular interactions in the crystals for starting materials and products. The dimerization and isomerization of unsaturated compounds as well as addition polymerization via a chain reaction mechanism are ideal sohd-state reactions, because they produce no leaving group during the reac-... 

Isomerization of unsaturated nitrogen-containing organic compounds, containing C=C double bonds, has been investigated less intensely than the isomerization of other related unsaturated compounds. Photoisomerization has been reported upon irradiation of a benzene solution of aqueous solution of its hydrochloride, and of the methiodide salt under nitrogen atmosphere. The corresponding cis-isomers are formed.308,309... 

L = P(CH3)3 or CO, oxidatively add arene and alkane carbon—hydrogen bonds (181,182). Catalytic dehydrogenation of alkanes (183) and carbonylation of benzene (184) has also been observed. Iridium compounds have also been shown to catalyze hydrogenation (185) and isomerization of unsaturated alkanes (186), hydrogen-transfer reactions, and enantioselective hydrogenation of ketones (187) and imines (188). 

The actions of photoexcited semiconductor particles on organic compounds under oxygen is of significant importance from both practical and basic aspects. Semiconductors like titanium dioxide and cadmium sulfide were shown to induce oxidation of olefins and aromatic hydrocarbons under oxygen, and also to sensitize isomerization of unsaturated systems. The mechanisms of these reactions are discussed. 

At the end of 1970 s we attempted an investigation of the action of semiconductor particles on medium sized organic compounds. In this article, we would like to describe some of the work done in our laboratory on the photocatalytic action of semiconductors on the oxidation of olefins and hydrocarbons, and on the isomerization of unsaturated systems. 

Adhikari S, Sprinz H, Brede 0 (2001) Thiyl radical induced isomerization of unsaturated fatty acids determination of equilibrium constants. Res Chem Intermed 27 549-559 Adhikary A, Bothe E, Jain V, von Sonntag C (2000) Pulse radiolysis of the DNA-binding bisbenzimid-azole derivatives Hoechst 33258 and 33342 in aqueous solution. Int J Radiat Biol 76 1157-1166 Akhlaq MS, von Sonntag C (1986) Free-radical-induced elimination of H2S from dithiothreitol. A chain reaction. J Am Chem Soc 108 3542-3544... 

Sprinz H, Schwinn J, Naumov S, Brede O (2000) Mechanism of thiyl radical-catalyzed isomerization of unsaturated fatty acids in homogeneous solution and in liposomes. Biochim Biophys Acta 1483 91-100... 

This conclusion is supported by observations of the isomerization of unsaturated hydrocarbons catalysed by potassium amide not only in ammonia solution (Shatenshtein and Vasil eva, 1954 Shatenshtein et al., 1954) but also by solid amides of alkali and alkaline-earth metals (Shatenshtein et al., 1958a). For example, diallyl rearranges to dipropenyl, pentene-1 to pentene-2, and 2-methylbutene-l to 2-methyl-butene-2. Subsequently, a further number of examples of isomerization... 

Ketones arise from phenols by isomerization of unsaturated alcohols (37). Palladium is the most suited for this type of reaction because of its high isomerization activity coupled with a very low rate of reduction of the resulting ketones (6). Excellent yields of ketones often may be obtained rhodium will give at times quite substantial yields of cyclohexanones (50-65% methylcyclohexanones from cresols) (38), but in other reductions such as resorcinol, little ketone accumulates over either rhodium or platinum under conditions where it is a major product over palladium (29). 

One general aspect to consider about intramolecular carbolithiation reactions is the fact that the isomerizations of unsaturated organolithiums could, in principle, proceed via... 

Isomerization of unsaturated compounds (I, 013-914 2, 336- 337 3. 233). The reaction of -methallyl chloride (I) with sodamide in boiling dioxane or di-n-butyl ether affords a mixture rf methylenecyclopropane (2) and 1-methylcyclopropene (3). Treatment of the mixture with potassium t-butoxide in DMSO affords methylenecyclo-propane in a purity of 98.3-98.6% (glc analysis). ... 

An interesting consequence of the base-catalyzed isomerization of unsaturated ketones described in Problem 22.37 is that 2-substituted 2-cyclopentenones can be interconverted with 5-substituted 2-cyclopentenones. Propose a mechanism for this isomerization. 

The isomerization of allylic alcohols to carbonyl compounds is usually carried out in the presence of transition-metal complexes under rather drastic conditions. The joint use of PTC and metal-complex catalysis creates a simple, mild, and efficient method for the isomerization of unsaturated alcohols [183]. Allylic alcohols are converted to ketones in a PT system with a Rh complex. An ion-pair [R4N] [RhCl4] (see Section 3.2.4.2.1) is also effective for the isomerization of allylic alcohols as well as allylarenes [184], Another example of PTC isomerization is the transformation of allylic alcohols, RCH(OH)CH=CFl2, to ketones, RCOCH2CH3 [185]. 

In 1989 Curran and co-workers reported on a photocatalytically induced free-radical cyclization leading to various cyclic, bi-, or polycyclic carbocycles (fused and spiro) via isomerization of unsaturated iodides (alkenes, alkynes) [63]. This corresponds to the nonreductive variant of the tin hydride method. Under sunlight irradiation and in the presence of 10 mol% hexabutylditin, a-iodo esters, ketones, and malonates are efficiently transformed via an iodide atom transfer chain mechanism (eq. (4)). 

Isomerization of unsaturated compounds. Raphael reported the finding that a 10% solution of the reagent in refluxing diethylene glycol dimethyl ether (b.p. 161°) rearranges diacetylenes to aromatic hydrocarbons in yields of about 65%. Thus 1,6-heptadiyne affords toluene. 

ThiyI radicals are important reactants in several enzymes and form in vivo during conditions of oxidative stress [6]. They have been considered for a long time as rather unreactive species. However, recently several reactions of thiyi radicals with biomolecules have been described (catalysis olcis-trans isomerization of unsaturated fatty acids, addition to the pyrimidine bases C5-C6 double bonds, and hydrogen abstraction from polyunsaturated fatty acid, thymine and peptide C -H and side chain C-H bonds) [7]. More recently, the intramolecular addition of peptide cysteine thiyi radicals (CysS ) to phenylalanine (Phe) yielding alkylothio-substituted cyclohexadienyl radicals was demonstrated in the peptides Phe-Cys and Phe-Gly-Cys-Gly (Fig. 2) [8]. 

In due consideration of these results, we have decided to employ electrostatic forces to achieve a large reversible deformation of gels. The electrostatic force is expected to be a more effective driving force for the conformational changes of polymer chains than trans-cis geometrical isomerization of unsaturated linkages. The second part describes the photostimulated dilation of polymer gels. 

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