Isomerization and adduction

Isomerization and Adduction of Hydroaromatic Systems at Conditions of Coal Liquefaction... 

Numerous implications on the fundamental chemistry of coal liquefaction can be drawn from the observed reaction of solvent isomerization and adduction. The literature indicates that... 

Cronauer, D. C., D. M. Jewell, Y. T. Shah, R. J. Modi and K. S. Seshadri. Isomerization and Adduction of Hydrogen Donor Solvents under Conditions of Coal Liquefaction. Ind. Eng. Chem. Fundam., 1979, 18, 368-376. 

With alkyl- and arylsilanes, concurrent isomerization and hydrosilylation occur, but the rates of both processes fall away rapidly due to some reduction to the metal such deactivation is temperature-dependent, and high yields of adduct are obtained with these silanes when additions are carried out slowly at ambient temperature. 

In some cases we may benefit from using an external agent to carry out the desired separation through crystallization. Thus, in the case of isomeric and non-isomeric mixtures of close-boiling acidic or basic materials we may use a suitable base or acid to carry out dissociative extractive crystallization, akin to dissociative extraction referred to in Section 4.2.1. For instance, for a mixture of p- and m-cresol or p-cresol and 2,6-xylenol we may use a base like anhydrous piperazine to obtain a precipitate of relatively pure p-cresol salt of piperazine, which can then be filtered and subjected to recovery of piperazine for recycle. Similarly, we may add a substance which forms an adduct with the desired substance. 

Proniewicz LM, Paeng IR, Nakamoto K. 1991. Resonance raman spectra of two isomeric dioxygen adducts of iron(II) porphyrins and rr-cation radical and nonradical oxoferryl porphyrins produced in dioxygen matrixes Simultaneous observation of more than seven oxygen isotope sensitive bands J Am Chem Soc 113 3294. 

Preparative details and extensive i.r., n.m.r., and mass spectra have been described for the phosphoranes (87).48 These phosphoranes have a TBP structure, and for (87a)—(87c) their n.m.r. spectra are temperature-independent, and indicate that the fluorines bonded to phosphorus are equivalent. The authors have suggested an explanation based on rapid intramolecular isomerization, and discussed the possibility that a facile TR pathway exists for this process.46 Octahedral adduct formation between (87) and fluoride ion or trimethylphosphine has also been described,46 as shown in (88). 

Similar schemes can be developed easily for analogous reactions of acceptor-substituted polyenes. For example, a triene with an acceptor group in 1-position can form six regioi-someric products of Michael addition and electrophilic capture, and each of these exists as E/Z stereoisomers, diastereomers and/or enantiomers. Thus, reactions of this type are only useful if both the regio- and stereoselectivity can be controlled fortunately, only one isomeric Michael adduct is formed in many cases. This is true in particular for polyunsaturated Michael acceptors which bear at least one triple bond besides one or more double bonds. An additional feature of the latter substrate type is that nucleophilic additions can... 

An additional important observation that (Z)-enolates exhibit erythro diastereoselection was made by Dubois and Fellmann (5b). Their investigation demonstrated that the magnesium enolate 24a (20°C, Et2 0) condensed with benzaldehyde under kinetic conditions to give exclusively the erythro diastereomer 25E (R3 = Ph, E T>95 5), and upon prolonged equilibration afforded the isomeric threo adduct (T E > 95 5) (eq. [ 15]). Heathcock has reported... 

The 7-azaquadricyclane (77), like its precursor (12), shows evidence in the NMR spectrum of restricted rotation about the N-CO bond. All the 7-heteroquadricyclanes, 76-79, are thermolabile, and they rearrange very readily to the corresponding azepines (80) or oxepin (81). (In another instance the 7-oxabicyclo[4.1.0] valence-bond tautomer was obtained instead. ) In appropriate conditions the addition of acetylenic esters (methyl propiolate and dimethyl acetylene-dicarboxylate) competes successfully with the isomerization and gives the ca o-tricyclic adducts 82 or 83. " °... 

The QSAR data show that glucuronidation can be either a detoxification or bioactivation mechanism, depending chemical structure. For N SAIDs, it appears to be mostly a detoxification mechanism. Nonetheless, the toxicity of acyl glucuronide and glucoside adducts (espedally as it relates to isomerization and protein adduct formation) must be considered when designing carboxylic acids [38]... 

The reaction has been carried out using HCI either neat or in acetic acid,84 or in the presence of HgCh,83 BiCla86 or Me4NCl.M In acetic acid, mixtures of syn and anti adducts are produced,84 but reactions catalyzed by HgCl2 proceed by stereospecific anti addition.83-87 The reaction of r-butylacetylene affords the expected vinylic chloride, plus a mixture of isomeric dichloride adducts.84-88 The hydrochlorination of phenylacetyiene produces mixtures of syn and anti adducts in which the ratio is significantly affected by the solvent and catalyst used.84-89-90... 

Under similar conditions 45 reacts with methanol, n-butylamine, and aniline to produce mixtures of 1-naphthol and the two isomeric trans adducts. 

Vieira AJSC, Steenken S (1987a) Pattern of OH radical reaction with 6- and 9-substituted purines. Effect of substituents on the rates and activation parameters of unimolecular transformation reactions of two isomericOH adducts. J PhysChem 91 4138-4144 Vieira AJSC, Steenken S (1987b) Pattern of OH radical reaction with N6,N6-dimethyladenosine. Production of three isomeric OH adducts and their dehydration and ring opening reactions. J Am Chem Soc 109 7441-7448... 

Vieira AJSC, Steenken S (1990) Pattern of OH radical reaction with adenine and its nucleosides and nucleotides. Characterization of two types of isomeric OH adduct and their unimolecular transformation reactions. J Am Chem Soc 112 6986-6994 Vieira AJSC, Steenken S (1991) Pattern of OH radical reaction with N6,N6,9-trimethyladenine. Dehy-droxylation and ring-opening of isomeric OH-adducts. J PhysChem 95 9340-9346 Vieira AJSC, Candeias LP, Steenken S (1993) Hydroxyl radical induced damage to the purine bases of DNA in vitro studies. J Chim Phys 90 881-897... 

A transient also occurs in the reaction of 2,4-dinitrophenyl chloride (3) with sodium hydroxide in aqueous DMSO, Scheme 9.2 [15]. Isomeric a-adducts, 4 and 5, formed relatively rapidly from 3, are cul de sac species and detectable by UV-vis spectroscopy. A slower separate reaction of 3 yields the phenolate, presumably via intermediate 6, which did not accumulate to UV detectable concentrations. 

Table 9 Quantum Yield of 02 Generation (ISc) by Isomeric Bis-Adducts (34,35,36)...

Mass spectral analysis showed that the two products were isomeric and correspond to an adduct of C6o combined with benzene and photolytically generated ethoxycarbonylnitrene. Control experiments confirmed the formation of N-ethoxy-carbonylazepine which underwent further photochemical [2 + 4] and [2 + 6] cycloaddition reactions with C6o leading to the observed products. 

Figure 17 Mono (50) and regio-isomeric bis-adducts (51, ( )-52 and ( )-53) formed by Bingel cyclopropanation of [70]fullerene. Also shown are Newman-type projections looking down the C s-symmetry axis of the C70 core on to the two polar pentagons, which show the relative orientations of the addends.

Figure 21 Isomerization and retro-cyclopropanation reactions of bis-Bingel adducts of [60]fullerene induced electrolytically.

Figure 30 Preparation of the pure enantiomers of D2-C84 by a retro-Bingel reaction of the fourth and fifth fractions of the bis-adducts, and CD spectra of the diastereo-isomeric bis-adduct (top right) as well as of the fullerene enantiomers (bottom right) in CH2C12. The absolute configurations of the fullerene spheroids reflect the structural drawings, but have not been assigned experimentally. Reprinted from ref. [71] with permission from Wiley-VCH.

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